refactor: .gitignore migrations/

- We don't include migrations/ within other Django projects and thus,
we should standardize

- Adding to the gitignore will prevent people from committing the
directory in the future
Signed-off-by: David Haynes <dhaynes3@gmu.edu>

.gitignore

@@ -13,3 +13,4 @@ whats_open/secret_key.py
 whats_open/assets/
 static/admin/
 data
+whats_open/website/migrations
\ No newline at end of file