Rename lib file so gem name & plugin name are consistent

If you don't do this, we get the following:

lib/jekyll/site.rb:81:in `require':
  cannot load such file -- jekyll-last-modified-at (LoadError)
Update gemspec, too
Update require statement in spec_helper
Strip the format so the tailing spaces aren't included in the format
Mute call to ./script/bootstrap in ./script/cibuild
Merge branch 'parkr-rename'