Falling back to installed version if Github goes down

[mkargus]

The extension will get stuck on "Downloading Rojo..." and will not fallback to the already installed version if Github has issues.

Without a fallback in this case, it will throw Cannot read 'property' of find of undefined (#55) or HTTP status 500 errors. The extension will basically lock up until the user reload the windows.

[evaera]

This has been implemented in version 2 of the extension which is now the master branch