Bug 1206670 - Update dependencies for grunt build to latest versions

Package                      Current   Latest
grunt-contrib-cssmin          0.12.3   0.14.0
grunt-contrib-copy             0.8.0    0.8.1
grunt-contrib-uglify           0.9.1    0.9.2
grunt-usemin                   3.0.0    3.1.1

package.json

@@ -11,10 +11,10 @@
     "grunt-cache-busting": "0.0.11",
     "grunt-contrib-clean": "0.6.0",
     "grunt-contrib-concat": "0.5.1",
-    "grunt-contrib-copy": "0.8.0",
-    "grunt-contrib-cssmin": "0.12.3",
-    "grunt-contrib-uglify": "0.9.1",
-    "grunt-usemin": "3.0.0",
+    "grunt-contrib-copy": "0.8.1",
+    "grunt-contrib-cssmin": "0.14.0",
+    "grunt-contrib-uglify": "0.9.2",
+    "grunt-usemin": "3.1.1",
     "load-grunt-tasks": "3.2.0"
   },
   "devDependencies": {