fix migration

(transplanted from ad6797117b84145d9671b48b670ba05fd52fbbb0)

vispa/models/alembic/versions/43c7de99ad41_fix_credentials.py

@@ -17,10 +17,12 @@ import sqlalchemy as sa
 def upgrade():
     op.alter_column(u'workspace',
                     u'login_credencials',
-                    new_column_name=u'login_credentials')
+                    new_column_name=u'login_credentials',
+                    existing_type=sa.Boolean())
 
 
 def downgrade():
     op.alter_column(u'workspace',
                     u'login_credentials',
-                    new_column_name=u'login_credencials')
+                    new_column_name=u'login_credencials',
+                    existing_type=sa.Boolean())