chore(package): update grunt-contrib-uglify to version 4.0.1

Closes #278

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "grunt-contrib-clean": "^1.0.0",
     "grunt-contrib-concat": "^1.0.1",
     "grunt-contrib-cssmin": "^2.0.0",
-    "grunt-contrib-uglify": "^3.0.0",
+    "grunt-contrib-uglify": "^4.0.1",
     "grunt-fixpack": "^0.1.0",
     "jasmine-core": "^2.5.2",
     "karma": "^1.3.0",