docs: fixed typo in api.md for issue #1406

[gomathishankar37]

Summary

Proposed change: Fixed typo in FileSystemLoader Section of API Documentation Closes # 1406.

Checklist

I've completed the checklist below to ensure I didn't forget anything. This makes reviewing this PR as easy as possible for the maintainers. And it gets this change released as soon as possible.

• [x] Proposed change helps towards purpose of this project.
• [x] Documentation is added / updated to describe proposed change.
• [x] Tests are added / updated to cover proposed change.
• [x] Changelog has an entry for proposed change (if user-facing fix or feature).