Add prototype to descriptions

snippets/isAsyncFunction.md

@@ -5,7 +5,7 @@ tags: type,function,intermediate
 
 Checks if the given argument is an `async` function.
 
-- Use `Object.prototype.toString()` and `Function.call()` and check if the result is `'[object AsyncFunction]'`.
+- Use `Object.prototype.toString()` and `Function.prototype.call()` and check if the result is `'[object AsyncFunction]'`.
 
 ```js
 const isAsyncFunction = val =>