Update spec-runner to atom-mocha@2.0.3
Update spec-runner to atom-mocha@2.0.3

APM appears to have stopped packaging a module's entry-point implicitly,
unlike NPM (which always includes the file specified by the `main` field
in package.json). The latest version now lists `index.js` in the `files`
array, allowing package specs to run after `apm install`.

/cc @hansonw

DanBrooker/file-icons,file-icons/atom