Update VE core submodule to master (aaa8547)

New changes:
04d9484 Update OOjs UI to v0.1.0-pre (9aad824bd6)
981d86f Correctly update full size in MediaSizeWidget
e935a9f Demo page styling
e7b0557 FocusableNode: Use getClientRects()[0] instead of getBoundingClientRect()
7e7d5c1 Only allow slugs where paragraphs are allowed
8653a84 Localisation updates from https://translatewiki.net.
aaa8547 Update OOjs UI to v0.1.0-pre (b9d403a678)

Change-Id: Iaff1cda5605a397b78590c4f9b66d1e4d4d2d564