Support APT pinning by codename (e.g. squeeze, wheezy)
apt::key: trim keys to 8 chars to match with apt-key list, refs puppetlabs/puppetlabs-apt#100
Update travis and bundler

- Use ruby 2.0.0 instead of ruby-head
- Remove puppet 2.6 testing
- Add more bundler gems
Merge pull request #133 from benben/master

trim keys to 8 chars for matching with apt-key list (fix for #100)
Merge pull request #136 from hunner/change_specs

Update travis and bundler
Merge pull request #135 from CERIT-SC/master

Support APT pinning by codename