Upgrade to latest version of Jekyll

Thanks again for making this tool. I upgraded Jekyll from 0.12.0 to 1.1.2 and made various changes to get it working.

1. Used `bundle exec`
2. Added a rake task (`rake autogenerate`) due to auto in the config file being deprecated
3. Pass in the action to perform (build) to jekyll

You may want to consider a major version bump of bloggy if you merge this in.

Thanks!