add support for gitlab token

[obeleh]

This pr:

• Updates go-git and go-billy to v5
• Adds support for gitlab token (should also work with github but haven't tested that)

I first thought I would have to use http.TokenAuth but this except was present in go-git:

// IMPORTANT: If you are looking to use OAuth tokens with popular servers (e.g.
// GitHub, Bitbucket, GitLab) you should use BasicAuth instead. These servers
// use basic HTTP authentication, with the OAuth token as user or password.
// Check the documentation of your git server for details.

[obeleh]

I was curious if this PR is useful for you?