Add mocha compiler options

[t1gor]

Hi.

Thanks a lot for the package first place! Great job.

Nevertheless, I currently have an issue. I am tryint to cover with tests an ES6 jsx app (React). I used to be running tests with npm script:

./node_modules/bin/_mocha 
   --colors 
   --compilers js:babel-register 
   --require babel-polyfill 
   --recursive 
   --reporter mochawesome 
   --harmony 
   test/run-all-tests.js

Is there a way to pass params/options to mocha test runner within phabricator plugin and preserve those? Maybe I missed some line of possible configs ...