Prevent mlocate from indexing /var/lib/docker

The standard updatedb configuration will scan almost all directories on the host and index their contents, except those listed in the PRUNEPATHS configuration setting. As this includes the /var/lib/docker directory, the mlocate.db file can grow to several gigabytes quickly when running just a few dozen containers. Therefore this patch will exclude the /var/lib/docker directory from being indexed as well.
Merge pull request #17 from rojaro/patch-1

Prevent mlocate from indexing /var/lib/docker
Merge pull request #15 from AlbanAndrieu/master

Add docker.io for Ubuntu 14.04.1 LTS (trusty)
Updated readme
Use latest docker in Ubuntu 14.04
Merge pull request #21 from elventear/trusty_docker_fix

Use latest docker in Ubuntu 14.04