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

Closes #19

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "grunt-contrib-htmlmin": "^2.4.0",
     "grunt-contrib-imagemin": "^2.0.1",
     "grunt-contrib-jshint": "^1.1.0",
-    "grunt-contrib-uglify": "^3.0.1",
+    "grunt-contrib-uglify": "^4.0.1",
     "grunt-contrib-watch": "^1.0.0",
     "grunt-filerev": "^2.1.2",
     "grunt-google-cdn": "^0.4.3",