Update ChangeLog - Showing as UNRELEASED rather than 3.1.8

[lrljoe]

All Submissions:

• [ ] Have you followed the guidelines in our Contributing document?
• [ ] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Feature Submissions:

1. [ ] Does your submission pass tests and did you add any new tests needed for your feature?
2. [ ] Did you update all templates (if applicable)?
3. [ ] Did you add the relevant documentation (if applicable)?
4. [ ] Did you test locally to make sure your feature works as intended?

Changes to Core Features:

• [ ] Have you added an explanation of what your changes do and why you'd like us to include them?
• [ ] Have you written new tests for your core changes, as applicable?
• [ ] Have you successfully ran tests with your changes locally?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a0d8411) 88.67% compared to head (cedd4bf) 88.67%. Report is 11 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1621 +/- ## ========================================= Coverage 88.67% 88.67% Complexity 1354 1354 ========================================= Files 106 106 Lines 3189 3189 ========================================= Hits 2828 2828 Misses 361 361 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.