Does not work with API v4

[fr3no]

Summary

Seems like API v4 is not supported and since GitLab 11 API v3 is deprecated.
So it does not work anymore with current GitLab installations.

[fr3no]

Updating die API request from v3 to v4 in requests.go fixes the connecting issue but still returns an empty csv file. Not sure, but there might be some more things that need to be fixed due to changes in the API (see https://docs.gitlab.com/ee/api/v3_to_v4.html).