Fix force sync only syncing 25 contacts.
Fix force sync only syncing 25 contacts.

This was caused by using getGroupContacts, which uses CiviCRM's API which
defaults to 25 records (silently, I might add).

giant-rabbit/com.giantrabbit.civimailchimp,giant-rabbit/com.giantrabbit.civimailchimp,giant-rabbit/com.giantrabbit.civimailchimp