Update POST to PUT in main spec for continue exchange endpoint.

Author: msporny

index.html

@@ -569,7 +569,7 @@ <h4>Continue Exchange</h4>
         </p>
 
         <div class="api-detail"
-          data-api-endpoint="post /exchanges/{exchange-id}/{transaction-uuid}"></div>
+          data-api-endpoint="put /exchanges/{exchange-id}/{transaction-uuid}"></div>
       </section>
 
     </section>