Pending build status from Jenkins not getting updated in GitLab when running concurrent builds during merge requests

## Issue
Pending build status from Jenkins not getting updated in GitLab when running concurrent builds during merge requests

### Context
- **Gitlab plugin version**: 1.5.11
- **Gitlab version**: GitLab Enterprise Edition 11.5.3-ee
- **Jenkins version**: 2.138.3
- **Job type**: Pipeline

### Problem description
I'm running concurrent builds triggered with merge requests. I have checked **Do not allow concurrent builds** for queuing the builds. When the first merge request is made, a build is triggered and the build status is displayed on the merge request widget UI. Immediately, a second merge request is made and the build is kept on queue with a pending state, but the second build status, which is pending is not displayed on the merge request widget UI and the merge button is active which is not desired.