Fix syntax error

Adds a missing single quote thus fixing a syntax error.

Author: danielstopp

README.md

@@ -2090,7 +2090,7 @@ The `Dog` class receives two arguments, `name` since it extends `Animal`, and `s
 
 ```javascript
 // index.js
-console.log('running index.js);
+console.log('running index.js');
 import { sum } from './sum.js';
 console.log(sum(1, 2));