Bump to 0.15.0
This includes:
- gitlab-org/gitlab-triage!80
- gitlab-org/gitlab-triage!81
- gitlab-org/gitlab-triage!82
- gitlab-org/gitlab-triage!83
- gitlab-org/gitlab-triage!85
- gitlab-org/gitlab-triage!86
The list was extracted from git log v0.14.1.. --merges