Address lint issue

pyramid_oereb/contrib/data_sources/standard/models/__init__.py

@@ -16,7 +16,7 @@
 
 
 from sqlalchemy import Column, ForeignKey
-from sqlalchemy import String, Integer, Float, Date, Boolean
+from sqlalchemy import String, Integer, Float, Date
 from geoalchemy2.types import Geometry as GeoAlchemyGeometry
 from sqlalchemy.orm import relationship
 from sqlalchemy_utils import JSONType