Update i18n shim

A performance issue was fixed in the shim(s) generated by
generateJsonI18n.php, so it needed to be updated.

Change-Id: Ice9c5ee1d2b9c749e4fbb012ac545c65a8ee4240
Reviewed-on: https://gerrit.wikimedia.org/r/128011
Reviewed-by: L10n-bot <l10n-bot@translatewiki.net>
Tested-by: L10n-bot <l10n-bot@translatewiki.net>