fix: add post_meta 301 fix

[ShoGinn]

This PR gets after the issue described #314

Changes / fixes

Add a trailing slash to remedy this.

Checklist

Ensure you have checked off the following before submitting your PR.

• [x] tested locally with the latest release of Hugo. This requirement is a standard
• [ ] added new dependencies
• [ ] updated the [docs]() ⚠️

[chipzoller]

Thanks!