[Emacs] Fix typo.

Change-Id: Ief8ad1d4de57bfcbce779c78779270eb5b4b0224
Signed-off-by: Wei-Chung Wen <morisato3711@gmail.com>
[Emacs] Enable undo-tree and add redo+.

Change-Id: Ia0afe68cb26a2fc6ab20014f57e4c7e65badcd59
Signed-off-by: Wei-Chung Wen <morisato3711@gmail.com>