Update CONTRIBUTING.md

[codyrobert]

Fixes a titch of a typo.

Description

Please include a summary of the change and which GitHub issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Type of change

Please describe the type of change.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] TestUtmDotCodesActivation
• [ ] TestUtmDotCodesAjax
• [ ] TestUtmDotCodesIntegration
• [ ] TestUtmDotCodesShortenBitly
• [ ] TestUtmDotCodesShortenRebrandly
• [ ] TestUtmDotCodesUnit

Test Configuration:

• WordPress version:
• PHP version:
• MySQL version:

Checklist:

• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [x] I had fun writing this code

[chrislarrycarl]

Ta mate.