Allow auto version bump for cookbooks

[drpebcak]

thor version:bump auto does not work with chef cookbooks as it bumps build number (chef only allows for major, minor, and patch).

An option like thor version:bump chef_auto would be appreciated to bump the patch version unless otherwise specified in the commit message.

[ivey]

The -d flag sets the default if nothing was found in the commit logs:

thor version:bump auto -d patch

[drpebcak]

Beautiful! Thank you!