Docker container for building LibreOffice

[Bernardo Sulzbach]

Try to do a "apt-get update" before doing the "apt-get -y build-dep...".

I am not a professional Docker user but I would say this is already
being done, twice.

That guy's dockerfile:
https://github.com/FreeSoft-AL/libreoffice-compile/blob/master/docker/Dockerfile
(update at line 4, build-dep at line 9)

And the dockerfile that seems to run before his
https://github.com/tianon/dockerfiles/blob/4d24a12b54b75b3e0904d8a285900d88d3326361/sbin-init/ubuntu/upstart/14.04/Dockerfile
(apt-get update at line 7)