frontend: fix compile error due to bad type

This failed to compile due to a mis-match of types with TypeScript 4.x.
fixes #168.

{{cookiecutter.project_slug}}/frontend/src/views/Login.tsx

@@ -51,7 +51,7 @@ export const Login: FC = () => {
         setError(err.message);
       } else {
         // handle errors thrown from backend
-        setError(err);
+        setError(String(err));
       }
     }
   };