Code Cleanup : Regex for github.com and GHE can be unified to a single one

[kavishdahekar]

Currently, the findGitSlug method relies on two separate regexes for identifying a github.com or a GHE domain from a given repo URL.

1. Although findGitSlug returns either "CodeCommit", "GitHub" or "GitHubEnterprise" - this return value is never used elsewhere.
2. The code does not differentiate between github.com and GHE domain elsewhere, so a single regex is sufficient to extract both : ^https?://([^/]+)/(.+)/(.+?)(?:\.git)?$

If acceptable, I would be happy to make this fix and modify the tests.