Added bzip2 to requirements

bzip2 is needed to extract .tar.bz2 archives. If not installed, the extraction won't work and does mess up the phpMyAdmin folder:

root@test:~# tar xjf phpMyAdmin-4.0.0-all-languages.tar.bz2
tar (child): bzip2: Cannot exec: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
Merge pull request #2 from patschi/patch-1

Added bzip2 to requirements