use Psr17FactoryDiscovery instead of deprecated MessageFactoryDiscovery

Author: seanms734

src/Client.php

@@ -26,7 +26,7 @@
 use Facebook\Exception\SDKException;
 use Http\Client\HttpClient;
 use Http\Discovery\HttpClientDiscovery;
-use Http\Discovery\MessageFactoryDiscovery;
+use Http\Discovery\Psr17FactoryDiscovery;
 
 class Client
 {
@@ -189,7 +189,7 @@ public function sendRequest(Request $request)
         list($url, $method, $headers, $body) = $this->prepareRequestMessage($request);
 
         $psr7Response = $this->httpClient->sendRequest(
-            MessageFactoryDiscovery::find()->createRequest($method, $url, $headers, $body)
+            Psr17FactoryDiscovery::findRequestFactory()->createRequest($method, $url, $headers, $body)
         );
 
         static::$requestCount++;