folder_branch_ops: fix typo in comment
folder_branch_ops: fix typo in comment

Suggested by songgao.

Issue: #1741

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs