fix typo in 06-promisify article.md

promisiefy -> promisify

Author: ZhaoMuwei

1-js/11-async/06-promisify/article.md

@@ -82,7 +82,7 @@ The code may look a bit complex, but it's essentially the same that we wrote abo
 
 A call to `promisify(f)` returns a wrapper around `f` `(*)`. That wrapper returns a promise and forwards the call to the original `f`, tracking the result in the custom callback `(**)`.
 
-Here, `promisiefy` assumes that the original function expects a callback with exactly two arguments `(err, result)`. That's what we encounter most often. Then our custom callback is in exactly the right format, and `promisify` works great for such a case.
+Here, `promisify` assumes that the original function expects a callback with exactly two arguments `(err, result)`. That's what we encounter most often. Then our custom callback is in exactly the right format, and `promisify` works great for such a case.
 
 But what if the original `f` expects a callback with more arguments `callback(err, res1, res2, ...)`?