update go-gitlab version >= 0.29.0

[LAKostis]

go-gitlab bundled with atlantis is very outdated and doesn't work very well with V4 API. Sometimes gitlab server could reply with error 500 and request should retry but this behavior was implemented only in version 0.29.0 (xanzy/go-gitlab#800)

Currently, our atlantis losing POST data and won't return anything back on apply command which causing problems with CI usage.

Cheers

[LAKostis]

Example error with current version:

2020/08/05 16:00:28+0000 [EROR] command_runner.go:426 xxxxxxxx: Unable to comment: POST https://gitlab.com/api/v4/projects/xxxxxxx/notes: 500 {message: 500 Internal Server Error}

[lkysow]

@LAKostis can you try with runatlantis/atlantis:latest? I've merged the update PR.

[LAKostis]

@lkysow sorry, was busy last week. Tested :latest changes in our projects, no regressions observed. Haven't seen 500 errors from gitlab either :)