fix the inconsistent casing of meta files

[hyounesy]

Proposed change(s)

While renaming the source files in https://github.com/Unity-Technologies/URDF-Importer/pull/126 , git had not detected the change in the casing of the meta files. Resulting in warnings like the following in Unity Editor when making a fresh checkout:

Asset file 'Packages/com.unity.robotics.urdf-importer/Editor/MenuItems/CompareUrdf.cs.meta' and meta file 'Packages/com.unity.robotics.urdf-importer/Editor/MenuItems/CompareURDF.cs.meta' has inconsistent casing.

This PR is to fix the casing for the four affected files.

Useful links (GitHub issues, JIRA tickets, forum threads, etc.)

https://github.com/Unity-Technologies/URDF-Importer/pull/126

Types of change(s)

• [ ] Bug fix
• [ ] New feature
• [x] Code refactor
• [ ] Documentation update
• [ ] Other (please describe)

Testing and Verification

NA

Test Configuration:

• Unity Version: Unity 2020.3.13f1
• Unity machine OS + version: macos Catalina 10.15.7

Checklist

• [x] Ensured this PR is up-to-date with the dev branch
• [x] Created this PR to target the dev branch
• [ ] Followed the style guidelines as described in the Contribution Guidelines
• [ ] Added tests that prove my fix is effective or that my feature works
• [ ] Increased the test coverage criteria by 3%
• [ ] Updated the Changelog and described changes in the Unreleased section
• [ ] Updated the documentation as appropriate