Update the package repo_url field when it has changed

[marcusmoore]

As mentioned in this PR comment we are capturing GitLab repositories that are returning redirects (when a user has changed their username) so we can grab changes, like readme updates, but not properly storing the new url for the repository locally.

The Package model has both url and repo_url fields which are used differently throughout the app. Currently, the url field is updated when a redirect is followed but the repo_url is not.