make sure we are dealing with bytestrings when migrating

elasticgit/commands/gitmodel.py

@@ -49,7 +49,7 @@ def run(self, working_dir, module_name):
             for data_record in data_records:
                 record = model_class(data_record)
                 storage_manager.store(record, 'Migrated %s.' % (
-                    record.uuid,))
+                    record.uuid.encode('utf-8'),))
                 records.append(record)
 
             # Save the schema in the new module's dir