Update part8b.md

Changed error.graphQLErrors[0].error.errors to error.graphQLErrors[0].message because message doesn't exist 
in first path

Author: ancxanas

src/content/8/en/part8b.md

@@ -600,8 +600,7 @@ const PersonForm = ({ setError }) => {
     refetchQueries: [  {query: ALL_PERSONS } ],
     // highlight-start
     onError: (error) => {
-      const errors = error.graphQLErrors[0].extensions.error.errors
-      const messages = Object.values(errors).map(e => e.message).join('\n')
+      const messages = error.graphQLErrors[0].message
       setError(messages)
     }
     // highlight-end