Use FileUtils.rmdir instead of `rm -rf`
Use FileUtils.rmdir instead of `rm -rf`

This prevents accidentally deletion of untracked files in the submodule
and is cross-platform compatible.

gnagel/overcommit,oxocode/overcommit,blech75/overcommit,blech75/overcommit,gnagel/overcommit,oxocode/overcommit,TheSooth/overcommit,TheSooth/overcommit