Update folly commit in HHVM OSS third-party

Summary: D1370893 requires folly code (`Format.h::sformat`) that is only available in a commit greater than the one pinned to the third-party folly submodule HEAD. Let's update it.

Test Plan: D1370893 will compile in open source.

Reviewers: sgolemon, liranuna, fredemmott, ptarjan

Reviewed By: ptarjan

Subscribers: folly@lists

Differential Revision: https://phabricator.fb.com/D1384493