Update autojump to v21.3.0 released 05 jan 2013

* Release v21.3.0:
  - `jumpapplet` removed.
  - performance improvements when using network mounts (e.g. sshfs)

* Release v21.2.0:

  - Add `jc` command (jump child). Jumps to a subdirectory of the
  current working directory.

/cc @wting