chore(package): update uglify-js to version 3.9.2

Closes #28

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
     "jsdom": "9.11.0",
     "mkdirp": "0.5.1",
     "mocha": "3.2.0",
-    "uglify-js": "2.7.5"
+    "uglify-js": "3.9.2"
   },
   "main": "index.js",
   "keywords": [