Bump jemoji to v0.3.0

Upgrades to Gemoji 2.0.
Also upgrades to HTML Pipeline 1.9 which is the only version
that supports Gemoji 2.0.

https://github.com/jekyll/jemoji/releases/tag/v0.3.0
Merge branch 'master' into jemoji-0-3-0
Merge pull request #80 from github/jemoji-0-3-0

jemoji 0.3.0