fix: Abstract Closure now captures thisArg

Thanks @waldemarhorwat.

Author: js-choi

spec.html

@@ -114,7 +114,7 @@ <h1><ins>Array.fromAsync ( _asyncItems_ [ , _mapfn_ [ , _thisArg_ ] ] )</ins></h
         <emu-alg>
           1. Let _C_ be the *this* value.
           1. Let _promiseCapability_ be ! NewPromiseCapability(%Promise%).
-          1. Let _fromAsyncClosure_ be a new Abstract Closure with no parameters that captures _C_ and _mapfn_ and performs the following steps when called:
+          1. Let _fromAsyncClosure_ be a new Abstract Closure with no parameters that captures _C_, _mapfn_, and _thisArg_ and performs the following steps when called:
             1. If _mapfn_ is *undefined*, let _mapping_ be *false*.
             1. Else,
               1. If IsCallable(_mapfn_) is *false*, throw a *TypeError* exception.