Fixed typo

Author: GrahamCampbell

src/Plugin.php

@@ -6,6 +6,7 @@
 
 use Http\Promise\Promise;
 use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
 
 /**
  * A plugin is a middleware to transform the request and/or the response.
@@ -24,8 +25,8 @@ interface Plugin
      *
      * @see http://docs.php-http.org/en/latest/plugins/build-your-own.html
      *
-     * @param callable(RequestInterface): Promise $next  Next middleware in the chain, the request is passed as the first argument
-     * @param callable(RequestInterface): Promise $first First middleware in the chain, used to to restart a request
+     * @param callable(ResponseInterface): Promise $next  Next middleware in the chain, the request is passed as the first argument
+     * @param callable(ResponseInterface): Promise $first First middleware in the chain, used to to restart a request
      *
      * @return Promise Resolves a PSR-7 Response or fails with an Http\Client\Exception (The same as HttpAsyncClient)
      */