update dependencies
style updates
CI updates:

* add Chef 12
* drop Ruby 1.9 support
* use Travis Docker support - thanks @helgi
* cache bundler
Merge pull request #236 from phlipper/updates

Miscellaneous updates
update root password check:

* use `mysqladmin version` vs. `ping` as it uses the proper exit code
add contribution from @helgi to the README
Merge pull request #237 from phlipper/better_root_pw

Better guard around update mysql root password
Install and configure pam_auth