JSONField.concat always uses json.dumps on parameters
Thanks, this is fixed.
```Python
from peewee import Model, PostgresqlDatabase
from playhouse.postgres_ext import BinaryJSONField

database = PostgresqlDatabase(database='postgres', autoconnect=True)

class Test(Model):
    x = BinaryJSONField(index=False)
    y = BinaryJSONField(index=False)
    class Meta:
        database = database

q = Test.select(Test.x.concat(Test.y)).dicts()
print(list(q))
```

This raises exception `TypeError: Object of type BinaryJSONField is not JSON serializable`.