Add missing quote for the initial value of the global object property (#18)

Author: arai-a

spec.html

@@ -150,7 +150,7 @@ <h1>The AsyncIterator Constructor</h1>
         <p>The <dfn>AsyncIterator</dfn> constructor:</p>
         <ul>
           <li>is <dfn>%AsyncIterator%</dfn>.</li>
-          <li>is the initial value of the *AsyncIterator* property of the global object.</li>
+          <li>is the initial value of the *"AsyncIterator"* property of the global object.</li>
           <li>is designed to be subclassable. It may be used as the value of an *extends* clause of a class definition.</li>
         </ul>