Fix documentation missing closing backticks

[jamesvl]

This was causing the 3.0.0 docs to not render the CSV.decode examples properly.

This PR addresses

• maybe: v3.0.1 module documentation missing on hexdocs.pm #114 (removes all warnings emitted during docs build process)

Open questions

• Not sure how you would like to handle versioning for docs-only changes, if it warrants a bump to 3.0.2 or not

Checklist

• n/a: Tests added
• n/a: Coverage increases or stays the same
• done: Docs updated
• not done: Changelog updated

[coveralls]

Coverage increased (+0.5%) to 100.0% when pulling da8cd70 on jamesvl:main into adc18c0 on beatrichartz:main.

[beatrichartz]

Thanks for this!