Fix ignore rule: _id -> doc_type
Fix ignore rule: _id -> doc_type

This got messed up in c0b129935588b1bc8f7ec5b58b522de067700c68. A false-positive test_migrate_attachments pass due to JSON-encoding error (see 38ccc8df0fe6f17837db4aa703310279fa48beb9) caused it not to be noticed.

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq