A workaround to use fudanchii/raw-request branch without changing the import path.

At least until https://github.com/plouc/go-gitlab-client/pull/8
accepted or Drone officially fork it to `drone/go-gitlab` or
when we have package management which can do something like this:

gom 'github.com/plouc/go-gitlab-client',
  :github => 'fudanchii/go-gitlab-client', :branch => 'raw-request'