Fix typo (#1061)

Fix typo

1-js/06-advanced-functions/05-global-object/article.md

@@ -58,7 +58,7 @@ That said, using global variables is generally discouraged. There should be as f
 
 We can test the global object for support of modern language features.
 
-For instance, test if a build-in `Promise` object exists (it doesn't in really old browsers):
+For instance, test if a built-in `Promise` object exists (it doesn't in really old browsers):
 ```js run
 if (!window.Promise) {
   alert("Your browser is really old!");