upgrade grunt-sass to 2.0.0 (#8808)

package.json

@@ -33,7 +33,7 @@
     "grunt-ng-annotate": "^3.0.0",
     "grunt-notify": "^0.4.5",
     "grunt-postcss": "^0.8.0",
-    "grunt-sass": "^1.2.1",
+    "grunt-sass": "^2.0.0",
     "grunt-string-replace": "~1.3.1",
     "grunt-systemjs-builder": "^0.2.7",
     "grunt-usemin": "3.1.1",