Fix trial sampling subject for go/no-go example (#35)

Author: banchan86

workflows/hobgoblin-reactiontime-samplediscreteuniform.bonsai

@@ -18,7 +18,7 @@
           <p1:Upper>1</p1:Upper>
         </Combinator>
       </Expression>
-      <Expression xsi:type="rx:PublishSubject">
+      <Expression xsi:type="rx:AsyncSubject">
         <Name>Trials</Name>
       </Expression>
       <Expression xsi:type="SubscribeSubject">