chore(gulp): gulp-minify-css -> gulp-clean-css

Author: Awk34

Diff for: app/templates/_package.json

@@ -65,7 +65,7 @@
     "jshint": "2.9.2",
     "gulp-livereload": "^3.8.0",
     "gulp-load-plugins": "^1.0.0-rc.1",
-    "gulp-minify-css": "^1.1.6",
+    "gulp-clean-css": "^2.0.6",
     "gulp-mocha": "^2.1.3",
     "gulp-ng-annotate": "^2.0.0",
     "gulp-ng-constant": "^1.1.0",