fix run-on sentence

Author: KennethKinLum

1-js/11-async/03-promise-chaining/article.md

@@ -72,7 +72,7 @@ promise.then(function(result) {
 });
 ```
 
-What we did here is just several handlers to one promise. They don't pass the result to each other, instead they process it independently.
+What we did here is just several handlers to one promise. They don't pass the result to each other; instead they process it independently.
 
 Here's the picture (compare it with the chaining above):