Updating WordPress core, and wp-evidence-hub sub-modules

* https://github.com/WordPress/WordPress/tree/3.8-branch
* v3.8.1, -01-23: https://github.com/WordPress/WordPress/commit/831b3ca50dd98fdd0efe
* https://core.trac.wordpress.org/log/branches/3.8/src?rev=27325
* -02-26: https://github.com/mhawksey/wp-evidence-hub/commit/75218ec9957e6ff6905c