Update VE core submodule to master

Also update MWConverter.test.js for test util changes.

New changes:
863288b Update OOjs UI to v0.1.0-pre (af97c1caec)
0bb2404 Refactor converter test utils to run single test cases

Change-Id: I90273786ac186df3eec13270f94d655b605bfdc4
Merge "Update VE core submodule to master"