Custom GitHub status check URL for enterprise setups

[patrickhulce]

In order to use status checks on internal enterprise editions, the status check URL needs to be configurable.

[patrickhulce]

@sirMerr I see you've +1'd this issue. Would you be able to give the PR #181 a try to see if it solves this? I don't have access to an enterprise github instance to test, but it's been implemented for over a month :)

EDIT: open invitation to anyone else that bumps into this, we'd love help validating this solves the issue.