Reflect the real intention on the promise returned by the Plugin

Author: joelwurtz

src/Plugin.php

@@ -24,7 +24,7 @@ interface Plugin
      * @param callable         $next    Next middleware in the chain, the request is passed as the first argument
      * @param callable         $first   First middleware in the chain, used to to restart a request
      *
-     * @return Promise
+     * @return Promise Resolves a PSR-7 Response or fails with an Http\Client\Exception.
      */
     public function handleRequest(RequestInterface $request, callable $next, callable $first);
 }