Use valid css class names when pygments language contains invalid chars, eg html+jango
Added a link to the list of all tz database time zones
Protect against nil @lang before fixing for css class names.
Added Jekyll-Ordinal plugin to list of third-party plugins.

Closes #2150.

Signed-off-by: Parker Moore <parkrmoore@gmail.com>
Update history to reflect merge of #2150 [ci skip]
Merge pull request #994 from stephenmcd/master
Update history to reflect merge of #994 [ci skip]
Lock to cucumber v1.3.11 because 1.3.12 is failing like crazy.
Move test dir to inside tmp in this repo.
Merge pull request #2155 from jekyll/fix-cucumber
Update history to reflect merge of #2155 [ci skip]
Add a message and error out when Pygments returns nil.
Went with @stomar's suggestion
Add jekyll_figure plugin
Merge pull request #2158 from lmullen/patch-1
Update history to reflect merge of #2158 [ci skip]
Merge pull request #2148 from jekyll/error-when-pygments-errors
Update history to reflect merge of #2148 [ci skip]
Add travis_retry to config
Merge pull request #2160 from jpiasetz/travis