use double quotes instead of single quotes

Author: CaselIT

graphql/execution/utils.py

@@ -144,7 +144,7 @@ def get_argument_values(self, field_def, field_ast):
 
     def report_error(self, error, traceback=None):
         # type: (Exception, Optional[TracebackType]) -> None
-        logger.error('%s', error, exc_info=(type(error), error, getattr(error, 'stack', None) or traceback))
+        logger.error("%s", error, exc_info=(type(error), error, getattr(error, "stack", None) or traceback))
         self.errors.append(error)
 
     def get_sub_fields(self, return_type, field_asts):