chore(package): update uglifyjs-webpack-plugin to version 2.1.2

Closes #8

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "eslint": "^4.11.0",
     "jest": "^21.2.1",
     "title-case": "^2.1.1",
-    "uglifyjs-webpack-plugin": "^1.0.1",
+    "uglifyjs-webpack-plugin": "^2.1.2",
     "webpack": "^3.8.1"
   }
 }