fix: broken link "how object equality works" with updated URL

Author: jordijs

src/content/2/en/part2b.md

@@ -461,7 +461,7 @@ Note the use of the React developer tools extension in the picture above!
 
 <h4>2.7: The Phonebook Step 2</h4>
 
-Prevent the user from being able to add names that already exist in the phonebook. JavaScript arrays have numerous suitable [methods](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) for accomplishing this task. Keep in mind [how object equality works](https://www.joshbritz.co/posts/why-its-so-hard-to-check-object-equality/) in Javascript.
+Prevent the user from being able to add names that already exist in the phonebook. JavaScript arrays have numerous suitable [methods](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array) for accomplishing this task. Keep in mind [how object equality works](https://www.joshbritz.co/blog/why-its-so-hard-to-check-object-equality/) in Javascript.
 
 Issue a warning with the [alert](https://developer.mozilla.org/en-US/docs/Web/API/Window/alert) command when such an action is attempted: