Adding detection for Google Apps Script.

Google Apps Script is currently detected as Gosu, so I'm adding it in to try to improve detection. It's just JavaScript, but with a different file extension and access to some Google-provided libraries.

For in-the-wild examples, just about any result from [this search](https://github.com/search?utf8=%E2%9C%93&q=.gs&type=Repositories&ref=advsearch&l=Gosu) will bring up Google Apps Script examples that have been categorized as Gosu.  For specific examples, see [zipabox-gs-connector](https://github.com/ntrinh/zipabox-gs-connector), [cartos-gs](https://github.com/madtrick/cartos-gs), and [google-spreadsheet-to-RJM](https://github.com/smcavinney/google-spreadsheet-to-RJM).