R1:3bccb0dcf2bc

Add custom Cows and Figlet directories to .gitignore

Summary: These directories didn't get added to `.gitignore`, but should be.

Test Plan:
- Touched a dummy file in each directory.
- Ran `git status`.
- Didn't see the file show up.

Reviewers: chad, cspeckmim

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D14249