Update VE core submodule to master (af4b395)

New changes:
9145f1a Use String#slice instead of discouraged String#substr
a3b7fe4 bin: Update update-unicodejs.sh to parity with update-oojs.sh
d475ba6 Localisation updates from https://translatewiki.net.
af4b395 Localisation updates from https://translatewiki.net.

Change-Id: Ie2615f54c4aa48aaab39229e6169953f721620dc
Merge "Update VE core submodule to master (af4b395)"