docfx: docfx.console NuGet package does not work well with a class library with multiple items in

DocFX Version Used: 2.28.2

Template used: default

Steps to Reproduce:

1. Create a .NET Standard Class Library project and modify its <TargetFrameworks> tag to use multiple values like netstandard1.3;net452.
2. Add docfx.console NuGet package to this project.
3. Create a docfx.json file to include the following information,

{
    "metadata": [
      {
        "src": [
          {
            "files": [
              "*.csproj"
            ],
            "exclude": [ "**/bin/**", "**/obj/**" ],
            "cwd": "."
          }
        ],
        "properties": {
            "TargetFrameworks": "net452"
        },
        "dest": "obj/10.0.2/api",
        "shouldSkipMarkup": true
      }
    ],
    "build": {
      "content": [
        { "files": [ "**/*.yml", "api/*.md" ], "src": "obj/10.0.2", "dest": "10.0.2" }
      ],
      "globalMetadata": {
        "_appTitle": "Some Documentation",
        "_disableContribution": true,
        "_appFooter": " ",
        "_navRel": "../toc.html"
      },
      "template": [
        "default",
        "template"
      ],
      "overwrite": [
        { "files": [ "obj/10.0.2/overwrite/*.md" ] }
      ],
      "dest": "_site"
    }
  }

Expected Behavior: The documentation should be generated without any error.

Actual Behavior: docfx seemed to be called twice, and the second instance could not access the log file and crashed,

1>[17-12-10 04:36:38.791]Info:[MetadataCommand.ExtractMetadata]Using msbuild C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin as inner compiler.
1>[17-12-10 04:36:38.792]Error:System.IO.IOException: The process cannot access the file 'F:\sharpsnmplib\SharpSnmpLib\log.txt' because it is being used by another process.
1>   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
1>   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
1>   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
1>   at System.IO.StreamWriter.CreateFile(String path, Boolean append, Boolean checkHost)
1>   at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize, Boolean checkHost)
1>   at System.IO.StreamWriter..ctor(String path, Boolean append)
1>   at Microsoft.DocAsCode.Common.ReportLogListener..ctor(String reportPath, String repoRoot, String root)
1>   at Microsoft.DocAsCode.SubCommands.CommandCreator`2.Create(String[] args, ISubCommandController controller, SubCommandParseOption option)
1>   at Microsoft.DocAsCode.SubCommands.CompositeCommand..ctor(String[] args, ISubCommandController controller, CompositeOptions options)
1>   at Microsoft.DocAsCode.SubCommands.CommandController.Create()
1>   at Microsoft.DocAsCode.Program.ExecSubCommand(String[] args)
1>docfx 2.28.2.0
1>Copyright (C) 2017 Copyright c Microsoft docfx 2015-2017
1>This is open-source software under MIT License.
1>
1>
1>   Usage1: docfx <docfx.json file path> [-o <output folder path>]
1>
1>   Usage2: docfx <subcommand> [<args>]
1>
1>
1>
1>
1>
1>See 'docfx help <command> to read about a specific subcommand guide
1>
1>
1>    build           : Generate client-only website combining API in YAML files and conceptual files
1>    dependency      : Export dependency file
1>    download        : Download remote xref map file and create an xref archive in local.
1>    help            : Get an overall guide for the command and sub-commands
1>    init            : Generate an initial docfx.json following the instructions
1>    merge           : Merge .net base API in YAML files and toc files.
1>    metadata        : Generate YAML files from source code
1>    pdf             : Generate pdf file
1>    serve           : Host a local static website
1>    template        : List or export existing template
1>
1>
1>Build failed.
1>[17-12-10 04:36:38.830]Error:System.IO.IOException: The process cannot access the file 'F:\sharpsnmplib\SharpSnmpLib\log.txt' because it is being used by another process.
1>   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
1>   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
1>   at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
1>   at System.IO.StreamWriter.CreateFile(String path, Boolean append, Boolean checkHost)
1>   at System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize, Boolean checkHost)
1>   at System.IO.StreamWriter..ctor(String path, Boolean append)
1>   at Microsoft.DocAsCode.Common.ReportLogListener..ctor(String reportPath, String repoRoot, String root)
1>   at Microsoft.DocAsCode.SubCommands.CommandCreator`2.Create(String[] args, ISubCommandController controller, SubCommandParseOption option)
1>[17-12-10 04:36:38.950]Info:[MetadataCommand.ExtractMetadata]Loading projects...
1>   at Microsoft.DocAsCode.SubCommands.CompositeCommand..ctor(String[] args, ISubCommandController controller, CompositeOptions options)
1>   at Microsoft.DocAsCode.SubCommands.CommandController.Create()
1>   at Microsoft.DocAsCode.Program.ExecSubCommand(String[] args)
1>	0 Warning(s)
1>	1 Error(s)
1>[17-12-10 04:36:38.953]Verbose:[MetadataCommand.ExtractMetadata](F:/sharpsnmplib/SharpSnmpLib/SharpSnmpLib.csproj)Loading project F:/sharpsnmplib/SharpSnmpLib/SharpSnmpLib.csproj
1>C:\Users\lextm\.nuget\packages\docfx.console\2.28.2\build\docfx.console.targets(53,5): error MSB3073: The command ""C:\Users\lextm\.nuget\packages\docfx.console\2.28.2\build\..\tools\docfx.exe" "F:\sharpsnmplib\SharpSnmpLib\docfx.json" -o "" -l "log.txt" --logLevel "Verbose"" exited with code 1.
1>Done building project "SharpSnmpLib.csproj" -- FAILED.