chore(package): update grunt-contrib-uglify to version 4.0.0

Author: greenkeeper[bot]

package.json

@@ -16,7 +16,7 @@
     "grunt-contrib-clean": "^1.0.0",
     "grunt-contrib-concat": "^1.0.1",
     "grunt-contrib-copy": "^1.0.0",
-    "grunt-contrib-uglify": "^3.0.0",
+    "grunt-contrib-uglify": "^4.0.0",
     "grunt-contrib-watch": "^1.0.0",
     "grunt-eslint": "^19.0.0",
     "grunt-karma": "^2.0.0",