Fix incorrect old name for Asana auth provider in provider migration

Summary: The old class name isn't quite correct.

I'm just updating the migration rather than adding a new one to fix it since
this was very recently introduced and affects only installs using Asana auth,
so it's realistic that the number of affected installs might be 0.

Affected installs can use `--apply` to safely rerun the migration.

Auditors: joshuaspence