Make sure we check for PSR client

Author: Nyholm

src/HttpClientRouter.php

@@ -43,7 +43,7 @@ public function sendAsyncRequest(RequestInterface $request)
     /**
      * Add a client to the router.
      *
-     * @param HttpClient|HttpAsyncClient $client
+     * @param ClientInterface|HttpAsyncClient $client
      */
     public function addClient($client, RequestMatcher $requestMatcher): void
     {

src/PluginClient.php

@@ -73,7 +73,7 @@ public function __construct($client, array $plugins = [], array $options = [])
     public function sendRequest(RequestInterface $request): ResponseInterface
     {
         // If we don't have an http client, use the async call
-        if (!($this->client instanceof HttpClient)) {
+        if (!($this->client instanceof ClientInterface)) {
             return $this->sendAsyncRequest($request)->wait();
         }