fix typo, chapter 3, line 165

mwilc0x · web-flow · commit c90ba13d4bf6 · 2018-09-12T07:51:40.000-04:00
diff --git a/async & performance/ch3.md b/async & performance/ch3.md
@@ -162,7 +162,7 @@ With Promises, the `then(..)` call can actually take two functions, the first fo
 ```js
 add( fetchX(), fetchY() )
 .then(
-	// fullfillment handler
+	// fulfillment handler
 	function(sum) {
 		console.log( sum );
 	},
