Don't assume github.com, take the repo URL from the remote config

[jjrussell]

Hey, I love this package and use it all the time. I recently got a new job at a place that uses github enterprise with it's own URL. This change allows the remote URL to dictate where to browse to. It still works with github.com itself but also enterprise.

Thanks for this package. It's awesome.

[xuhdev]

You might wanna check out the more actively maintained browse-at-remote