Update i18n shim

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

Change-Id: I06fbee23d1fb74875697e5f63f2bd442287da6df
Reviewed-on: https://gerrit.wikimedia.org/r/128569
Reviewed-by: L10n-bot <l10n-bot@translatewiki.net>
Tested-by: L10n-bot <l10n-bot@translatewiki.net>