Adding Google Apps Script (.gs) as a JavaScript extension.
languages.yml: added an interpreter entry to Mercury section
Support for gradle files
add language grammar for Isabelle theorem prover
Merge branch 'master' into google-apps

Conflicts:
	lib/linguist/heuristics.rb
	lib/linguist/samples.json
Merge pull request #1798 from github/google-apps

Google apps
Merge pull request #1790 from pchaigno/gradle

Support for gradle files
Merge pull request #1698 from sebgod/add-mercury-interpreter

languages.yml: added an interpreter entry to Mercury section
Merge branch 'master' into isabelle-grammar

Conflicts:
	grammars.yml
Merge pull request #1800 from github/isabelle-grammar

Isabelle grammar
Add grammar for Nix
Merge pull request #1802 from wmertens/master

Add grammar for Nix