Doesn't work on 2.7

[Blake-]

The schema definition for finding_aid_language was updated for 2.7 here:

https://github.com/archivesspace/archivesspace/blob/master/common/schemas/resource.rb#L54

I think these need changed:

https://github.com/alexduryee/multiple_identifiers/search?q=finding_aid_language&unscoped_q=finding_aid_language