Jekyll 3 changes and fix for getting authors when not running from an interactive shell

[jessp01]

• In Jekyll 3, need to call: site.posts.docs instead of site.posts, otherwise this deprication warning will be emitted: Jekyll.logger.warn "Deprecation:", "Collection##{method} should be called on the #docs array directly."

See: jekyll-3.0.0/lib/jekyll/collection.rb

• When running git shortlog -se in a none interactive way, [i.e from a jekyll process launched with jekyll serve -P80 -H0.0.0.0 --watch, for example], one would get ENOTTY errors and it will not return data, specifying 'HEAD' solves that and it then works from both an interactive shell and from the jekyll lunched as described above.

[ahmetb]

@ivantsepp can we have your attention please?

[ivantsepp]

Thanks for your fix and sorry for the LONG delay. I've been out of it 😢 . released https://rubygems.org/gems/jekyll-git_metadata/versions/0.1.0. I used your git shortlog fix in https://github.com/ivantsepp/jekyll-git_metadata/commit/7ec03ab49159d79c96c258c54c959d73002fa8cc