Fix $size operator
Fix $size operator

The convert function was missing an array reference "[]" in the path.

BugzID: 46731

apache/couchdb-mango,cloudant/couchdb-mango,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,kxepal/couchdb-mango,fkaempfer/couchdb,fkaempfer/couchdb