Modified get_meta_box_url() to return a protocol agnostic uri

[Blindmikey]

HTTPS environments fail to load the asset on certain browsers due to http:// being a part of the uri. By being protocol agnostic, we play well with all environments.

[jtsternberg]

I like this. However, can you please keep with the contribution guidelines, namely submit PR's against the trunk branch, and follow WP (and CMB) coding standards? Thank you kindly.

[Blindmikey]

Awesome, I'd be happy to - will just have to read up on those guidelines. Will have more time over the weekend.

Yay for my first PR!

[jtsternberg]

thanks @Blindmikey! Now you're unstoppable. ;)