Rename App.js to app.js

I got this error on my browser (firefox and chrome): 

Failed to load resource: the server responded with a status of 404 (Not Found) http://localhost:3000/source/app.js

So renaming it to app.js fixed this.
Merge pull request #21 from JaycenH7/master

Rename App.js to app.js

Reviewed-By: Ben Combee (ben.combee@lge.com)