remove useless char "?" at the end of redirect_uri

[zhangethan]

it's not compatible with gitlab-ce 12.5, gitlab will return 401 when trying to get access_token.

Testing done

I tested it with gitlab 12.5 and 16.1

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[MarkEWaite]

The change looks reasonable to me, since the parameters list is empty, the URL encoded format will be empty as well.

I don't think that it is especially important to support GitLab 12, since GitLab has issued many security advisories for versions after it and is not providing security fixes for GitLab 12.

[krisstern]

Thanks @zhangethan for your contribution!