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

Author: greenkeeper[bot]

package.json

@@ -20,7 +20,7 @@
     "grunt-contrib-clean": "1.1.0",
     "grunt-contrib-copy": "1.0.0",
     "grunt-contrib-jshint": "1.1.0",
-    "grunt-contrib-uglify": "3.4.0",
+    "grunt-contrib-uglify": "4.0.0",
     "grunt-contrib-watch": "1.1.0",
     "grunt-postcss": "0.9.0",
     "grunt-replace": "1.0.1",