chore(package): update grunt-contrib-uglify to version 2.0.0

https://greenkeeper.io/

package.json

@@ -38,7 +38,7 @@
     "grunt-browserify": "^5.0.0",
     "grunt-contrib-clean": "^1.0.0",
     "grunt-contrib-jshint": "^1.0.0",
-    "grunt-contrib-uglify": "^1.0.1",
+    "grunt-contrib-uglify": "^2.0.0",
     "grunt-contrib-watch": "^1.0.0",
     "grunt-karma": "^2.0.0",
     "grunt-tslint": "^3.1.1",