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.

Author: cardoe

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

@@ -20,7 +20,7 @@ export const Home: FC = () => {
       const message = await getMessage();
       setMessage(message);
     } catch (err) {
-      setError(err);
+      setError(String(err));
     }
   };
 

{{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));
       }
     }
   };

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

@@ -48,7 +48,7 @@ export const SignUp: FC = () => {
           setError(err.message);
         } else {
           // handle errors thrown from backend
-          setError(err);
+          setError(String(err));
         }
       }
     }