More than the expected nr of notifications when using parallelism.

[arjan0307]

Describe the bug
When running a job in parallel, you get a notification for each executor, rather than one notification for the entire job.

To reproduce

1. Set up parallelism in circle.
2. Configure the mattermost circleci plugin according to the documentation.
3. Add - mattermost-plugin-notify/status: to the end of the steps part of a job, as described in the orb documentation.
4. Run a job on Circle
5. Get a notification for each executor in the parallel job

Expected behavior
Get one notification that informs whether the entire job failed or succeeded.