Bump uglifyjs-webpack-plugin from 1.1.8 to 1.2.0 in /www

Bumps [uglifyjs-webpack-plugin](https://github.com/webpack-contrib/uglifyjs-webpack-plugin) from 1.1.8 to 1.2.0.
- [Release notes](https://github.com/webpack-contrib/uglifyjs-webpack-plugin/releases/tag/v1.2.0)
- [Changelog](https://github.com/webpack-contrib/uglifyjs-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack-contrib/uglifyjs-webpack-plugin@v1.1.8...v1.2.0)

www/package.json

@@ -89,7 +89,7 @@
     "stylelint-config-standard": "^18.0.0",
     "stylelint-order": "^0.8.0",
     "stylelint-webpack-plugin": "^0.10.2",
-    "uglifyjs-webpack-plugin": "^1.1.8",
+    "uglifyjs-webpack-plugin": "^1.2.0",
     "url-loader": "^0.6.2",
     "webpack": "^3.11.0",
     "webpack-dev-server": "^2.11.1",

www/yarn.lock

@@ -8663,9 +8663,9 @@ uglifyjs-webpack-plugin@^0.4.6:
     uglify-js "^2.8.29"
     webpack-sources "^1.0.1"
 
-uglifyjs-webpack-plugin@^1.1.8:
-  version "1.1.8"
-  resolved "https://registry.yarnpkg.com/uglifyjs-webpack-plugin/-/uglifyjs-webpack-plugin-1.1.8.tgz#1302fb9471a7daf3d0a5174da6d65f0f415e75ad"
+uglifyjs-webpack-plugin@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/uglifyjs-webpack-plugin/-/uglifyjs-webpack-plugin-1.2.0.tgz#f706fa4c655000a086b4a97c7d835ed0f6e9b0ef"
   dependencies:
     cacache "^10.0.1"
     find-cache-dir "^1.0.0"