chore(package): update grunt-contrib-uglify to version 3.1.0 (#430)

package.json

@@ -44,7 +44,7 @@
     "grunt-contrib-clean": "^1.0.0",
     "grunt-contrib-concat": "^1.0.1",
     "grunt-contrib-jshint": "^1.1.0",
-    "grunt-contrib-uglify": "^2.0.0",
+    "grunt-contrib-uglify": "^3.1.0",
     "grunt-conventional-changelog": "^6.1.0",
     "grunt-conventional-github-releaser": "^1.0.0",
     "grunt-endline": "^0.6.1",