Update state immutably

Author: robmelfi

src/App.js

@@ -24,7 +24,8 @@ class App extends Component {
     };
 
     deletePersonHandler = ( personIndex ) => {
-        const persons = this.state.persons;
+        // const persons = this.state.persons.splice();
+        const persons = [...this.state.persons];
         persons.splice(personIndex, 1);
         this.setState({
             persons: persons