Fixed error output from runserver

This has been missed in commit 822d6d6dab (Refs #18325).

django/core/management/commands/runserver.py

@@ -123,7 +123,7 @@ class Command(BaseCommand):
                 error_text = ERRORS[e.args[0].args[0]]
             except (AttributeError, KeyError):
                 error_text = str(e)
-            sys.stderr.write("Error: %s" % error_text)
+            self.stderr.write("Error: %s" % error_text)
             # Need to use an OS exit because sys.exit doesn't work in a thread
             os._exit(1)
         except KeyboardInterrupt: