Release bump 1.8.1

[raghavaggarwal2308]

Summary

Fixes

• https://github.com/mattermost/mattermost-plugin-gitlab/pull/419
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/394
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/395
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/429
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/406
• https://github.com/mattermost/mattermost-plugin-gitlab/pull/416

[codecov[bot]]

Codecov Report

Attention: 29 lines in your changes are missing coverage. Please review.

Comparison is base (475df6a) 33.57% compared to head (7b17953) 33.71%.

Files	Patch %	Lines
server/plugin.go	0.00%	14 Missing :warning:
server/webhook/merge_request.go	70.00%	4 Missing and 2 partials :warning:
server/flow.go	0.00%	4 Missing :warning:
server/api.go	0.00%	3 Missing :warning:
server/command.go	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## release-1.8.1 #460 +/- ## ================================================= + Coverage 33.57% 33.71% +0.14% ================================================= Files 22 22 Lines 3929 3945 +16 ================================================= + Hits 1319 1330 +11 - Misses 2479 2482 +3 - Partials 131 133 +2 ```

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[mickmister]

Note that this branch does not have the changes from https://github.com/mattermost/mattermost-plugin-gitlab/pull/451, so we'll need to manually set the version number in plugin.json in this PR

[raghavaggarwal2308]

@mickmister Updated version in plugin.json