Swap grammar used for CSS highlighting (#3426)

* Swap grammar used for CSS highlighting

* Whitelist license of Atom's CSS grammar

* Explicitly declare grammar as MIT-licensed

Source: https://github.com/atom/language-css/blob/5d4af/package.json#L14

grammars.yml

@@ -234,8 +234,6 @@ vendor/grammars/cpp-qt.tmbundle:
 - source.qmake
 vendor/grammars/creole:
 - text.html.creole
-vendor/grammars/css.tmbundle:
-- source.css
 vendor/grammars/cucumber-tmbundle:
 - source.ruby.rspec.cucumber.steps
 - text.gherkin.feature
@@ -369,6 +367,8 @@ vendor/grammars/language-csound:
 - source.csound
 - source.csound-document
 - source.csound-score
+vendor/grammars/language-css:
+- source.css
 vendor/grammars/language-emacs-lisp:
 - source.emacs.lisp
 vendor/grammars/language-fontforge: