Release v2.1.8
Fixes #72 Supports conf-available/conf-enabled on Ubuntu 14
Merge pull request #73 from yannh/confenabled_support

Fixes #72 Supports conf-available/conf-enabled on Ubuntu 14
Update specs to run from unified Gemfile; update supported versions; add lint run

Uses the default rubies from travis and has a few comments why some
matrix slots are excluded.

Ignores the Gemfile.lock, since changing the Gemfile via env will break
bundle's --deployment mode on travis.
Add validation