Update json.py remove assert.

Author: WaVEV

django_mongodb/fields/json.py

@@ -67,7 +67,6 @@ def has_key_lookup(self, compiler, connection):
     for path in paths:
         keys.append(_has_key_predicate(path, lhs))
     if self.mongo_operator is None:
-        assert len(keys) == 1
         return keys[0]
     return {self.mongo_operator: keys}