browser-sync: Startup in "server" mode gives "UnhandledPromiseRejectionWarning" in Node 6.7.0

Issue details

When starting BrowserSync in “server” mode, the following warning is given:

(node:1362) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Exited with code 3

Steps to reproduce/test case

browserSync.init() with “server” option configured. Removing server option/configuration gets rid of warning.

Please specify which version of Browsersync, node and npm you’re running

• Browsersync [ 2.17.3 ]
• Node [ 6.7.0 ]
• Npm [ 3.10.3 ]

Affected platforms

• linux
• [? ] windows
• [? ] OS X
• [? ] freebsd
• [? ] solaris
• other (please specify which)

Browsersync use-case

• API
• Gulp
• Grunt
• CLI

If CLI, please paste the entire command below

{cli command here}

for all other use-cases, (gulp, grunt etc), please show us exactly how you’re using Browsersync

  browserSync.init({
      server: "./web",
      port: 8000,
      ui: {
        port: 8001
      }