HStoreField from playhouse.postgres_ext
My bad, I was using wrong db connection
`HStoryField.db_field` value seems to be incorrect. When creating model with HStoreField and trying to migrate it I get:
```
peewee.ProgrammingError: type "hash" does not exist
```
even though the hstore extension is installed. When I changed db_field to `'hstore'` value migration was applied without any problems.