init: "mediawiki.action.history.diff" -> "mediawiki.diff.styles"
init: "mediawiki.action.history.diff" -> "mediawiki.diff.styles"

Module was renamed in MediaWiki core. Old name still works for
backwards-compatible so it was safe to wait until after the new
version is deployed on all Wikimedia wikis.

Now that it is, we can migrate.

Closes #67.

Krinkle/mw-gadget-rtrc