use built in travis caching

also run bundle update to make sure the cache is not too old
Add benchmark for Jekyll.sanitized_path
Strip the drive name from both paths when checking the prefix.
Merge pull request #3075 from joshk/patch-1
Update history to reflect merge of #3075 [ci skip]
Add the contributors to the v2.5.0 release post.

I'm such a doofus for forgetting!!!!
New title for new times.
Merge pull request #3077 from jekyll/fix-windows-path-sanitation
Update history to reflect merge of #3077 [ci skip]
Use paginator.(next|previous)_page_path instead of just the number.

Closes #3074
Prepare a :gem: v2.5.1 release.
Merge pull request #3080 from jekyll/release-2-5-1

Release v2.5.1
Release :gem: 2.5.1
v2.5.1 was released on Nov 9, not Nov 8.
Update site history page with v2.5.1