Add note about TypeScript 2 support for non-null

Despite being a fan of Flow, I do think it's prudent for any recent comparison to include SOME features on the project timeline, including [non-nullable types](microsoft/TypeScript#7140) in version 2.

Author: rajington

2016_hhjs.html

@@ -281,6 +281,7 @@ <h3>TypeScript</h3>
 </code></pre>
 
         <p class="fragment">TypeScript does not catch this</p>
+        <p class="fragment">Added in TypeScript 2</p>
       </section>
 
         <section>