spec: Await next value with default map ƒ

Fixes #19 

CC: @nicolo-ribaudo.

Author: js-choi

spec.html

@@ -77,7 +77,7 @@ <h1><ins>Array.fromAsync ( _asyncItems_ [ , _mapfn_ [ , _thisArg_ ] ] )</ins></h
                 1. Set _mappedValue_ to Await(_mappedValue_).
                 1. IfAbruptCloseAsyncIterator(_iteratorRecord_, _mappedValue_).
                 1. Set _mappedValue_ to _mappedValue_.[[Value]].
-              1. Else, let _mappedValue_ be _nextValue_.
+              1. Else, let _mappedValue_ be Await(_nextValue_).
               1. Let _defineStatus_ be CreateDataPropertyOrThrow(_A_, _Pk_, _mappedValue_).
               1. If _defineStatus_ is an abrupt completion, return ? AsyncIteratorClose(_iteratorRecord_, _defineStatus_).
               1. Set _k_ to _k_ + 1.