Update article.md

Author: leviding

1-js/04-object-basics/07-optional-chaining/article.md

@@ -21,7 +21,7 @@ let user = {}; // a user without "address" property
 alert(user.address.street); // Error!
 ```
 
-That's the expected result. JavaScript works like this. As `user.address` is `undefined`, an attempt to get `user.address.street` fails with an error. 
+That's the expected result. JavaScript works like this. As `user.address` is `undefined`, an attempt to get `user.address.street` fails with an error.
 
 In many practical cases we'd prefer to get `undefined` instead of an error here (meaning "no street").