Allow Convertibles to be converted by >= 1 converters.
Update continuous-integration.md

Fix typo
Refactor based on jekyll-watch clean-up.

https://github.com/jekyll/jekyll-watch/pull/5
Bump jekyll-watch version to 1.1.
It's called Jekyll::Watcher
Remove tests for the Command.ignored_paths method which now lives in jekyll-watch.
Read in every Document's content as UTF-8
Add magic comments for UTF-8
Pass in options to File.open in Document.
Merge pull request #2720 from jekyll/read-in-utf8
Update history to reflect merge of #2720 [ci skip]
Merge pull request #2708 from felixkiss/patch-1
Update history to reflect merge of #2708 [ci skip]
Merge pull request #2716 from jekyll/reform-watch
Update history to reflect merge of #2716 [ci skip]
Merge pull request #2704 from jekyll/mult-converters
Update history to reflect merge of #2704 [ci skip]
Don't concat extnames in output for multiple converters
Specify Ruby Dev Headers on Installation docs page.

Closes #2728
Call #to_liquid before calling #to_json in jsonify filter.