Update uglify-js to version 2.7.3 🚀 (#3547)

* chore(package): update uglify-js to version 2.7.3

https://greenkeeper.io/

* update CHANGELOG

CHANGELOG.md

@@ -15,6 +15,7 @@ CHANGELOG
 * @gkatsev added slack badge to README ([view](https://github.com/videojs/video.js/pull/3527))
 * @gkatsev reverted back to qunitjs 1.x to unbreak IE8. Added es5-shim to tests ([view](https://github.com/videojs/video.js/pull/3533))
 * @gkatsev updated build system to open es5 folder for bundles and dist folder other users ([view](https://github.com/videojs/video.js/pull/3445))
+* greenkeeper updated uglify ([view](https://github.com/videojs/video.js/pull/3547))
 
 --------------------
 

package.json

@@ -92,7 +92,7 @@
     "qunitjs": "^1.23.1",
     "sinon": "^1.16.1",
     "time-grunt": "^1.1.1",
-    "uglify-js": "~2.3.6",
+    "uglify-js": "~2.7.3",
     "videojs-doc-generator": "0.0.1",
     "videojs-standard": "^5.2.0"
   },