fastlane: Fastlane command fails immediately becuase of mismatching json versions

New Issue Checklist

• Updated fastlane to the latest version
• I have read the Contribution Guidelines

Issue Description

Fastlane immediately quits when any version of json newer than the ruby bundle version is installed.

Complete output when running fastlane, including the stack trace and command used

/usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/specification.rb:2274:in `check_version_conflict': can't activate json-2.0.2, already activated json-1.8.3 (Gem::LoadError)
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/specification.rb:1403:in `activate'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:89:in `block in require'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:88:in `each'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:88:in `require'
    from /usr/local/lib/ruby/gems/2.3.0/gems/fastlane_core-0.52.0/lib/fastlane_core.rb:1:in `<top (required)>'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
    from /usr/local/lib/ruby/gems/2.3.0/gems/fastlane-1.104.0/lib/fastlane.rb:1:in `<top (required)>'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
    from /usr/local/Cellar/ruby/2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:68:in `require'
    from /usr/local/lib/ruby/gems/2.3.0/gems/fastlane-1.104.0/lib/fastlane/cli_tools_distributor.rb:14:in `take_off'
    from /usr/local/lib/ruby/gems/2.3.0/gems/fastlane-1.104.0/bin/fastlane:5:in `<top (required)>'
    from /usr/local/bin/fastlane:23:in `load'
    from /usr/local/bin/fastlane:23:in `<main>'

Configuration Files

Please copy the complete content of your Fastfile and any other configuration files you use below:

Fastfile:

update_fastlane

fastlane_version "1.95.0"

default_platform :ios

platform :ios do
  before_all do
    ENV["CRASHLYTICS_API_TOKEN"] = "key_here"
    ENV["CRASHLYTICS_BUILD_SECRET"] = "secret_here"
    ENV["MATCH_READONLY"] = "true"
    ENV["MATCH_FORCE_FOR_NEW_DEVICES"] = "true"
    ENV["GYM_CLEAN"] = "true"
    ENV["GYM_SILENT"] = "true"
    cocoapods
  end

  desc "Just build the project"
  lane :build do
    match(type: "development")
    gym(scheme: "ManchesterCareers", configuration: "Debug")
  end

  desc "Runs all the tests"
  lane :test do
    match(type: "development")
    scan(scheme: "ManchesterCareers")
  end

  desc "Make an internal Fabric Beta release"
  lane :internalbeta do
    increment_build_number
    match(type: "adhoc")
    gym(scheme: "ManchesterCareers")
    crashlytics(groups: "dreamrs-ios")
  end

  desc "Make an full Fabric Beta release"
  lane :beta do
    increment_build_number
    match(type: "adhoc")
    gym(scheme: "ManchesterCareers")

    puts "Enter release notes here, end input with ctrl-D"
    releaseNotes = $stdin.read
    crashlytics(groups: "dreamrs-ios, manchester-careers", notes: releaseNotes)
  end

Environment

fastlane version (run fastlane -v): fastlane 1.104.0

Do you use bundler to execute fastlane (i.e. bundle exec fastlane)? No

Do you use a Ruby environment manager (e.g. chruby, rbenv, rvm)? No