Automated checking of all .ckan files by travis.

Tested on pjf/CKAN-meta by having a repo full of good files (travis
passes), and another which includes a bad file (travis fails).

This means should any invalid CKAN files end up in the CKAN-meta
directory, we'll know about them!

You can see a sample output at:

https://travis-ci.org/pjf/CKAN-meta