cmds: refresh branch list when deleting branches

We were not updating the internal cached list of branches when
deleting branches.  This caused auto-complete to list the
deleted branch as an option even though it had been deleted.

Refresh the cached branch list when deleting branches.

Closes #365

Reported-by: Minarto Margoliono <lie.r.min.g@gmail.com>
Signed-off-by: David Aguilar <davvid@gmail.com>