Update to Github Pages 22

* github-pages (22 > 21)
  Changelog: https://github.com/github/pages-gem/releases
* jekyll-sass-converter (1.2.0 > 1.1.0)
* jekyll-sitemap (0.5.1 > 0.5.0)
* sass (3.3.14 > 3.3.12)
* posix-spawn (0.3.9 > 0.3.8)
* gemoji (2.0.1 > 2.0.0)