client: reorder guzzle version compatibility check (#328)

It's an edge case but, if two versions of guzzle is installed at the
same time, reordering and check the presence of
`\GuzzleHttp\Client::createRequest` method avoid errors.

lib/Client.php

@@ -80,7 +80,18 @@ public function send(RequestInterface $apiRequest)
      */
     private function buildRequest($apiRequest)
     {
-        if (class_exists('\\GuzzleHttp\\Message\\Request')) {
+        if (class_exists('\\GuzzleHttp\\Psr7\\Request')) {
+            return new \GuzzleHttp\Psr7\Request(
+                $apiRequest->getMethod(),
+                $apiRequest->getPath(),
+                ['Content-Type' => 'application/json'],
+                json_encode($this->buildBody($apiRequest))
+            );
+        }
+
+        if (class_exists('\\GuzzleHttp\\Message\\Request')
+            && method_exists($this->client, 'createRequest')
+        ) {
             $options = array_merge(
                 $this->requestOptions,
                 ['json' => $this->buildBody($apiRequest)]
@@ -92,15 +103,6 @@ private function buildRequest($apiRequest)
             );
         }
 
-        if (class_exists('\\GuzzleHttp\\Psr7\\Request')) {
-            return new \GuzzleHttp\Psr7\Request(
-                $apiRequest->getMethod(),
-                $apiRequest->getPath(),
-                ['Content-Type' => 'application/json'],
-                json_encode($this->buildBody($apiRequest))
-            );
-        }
-
         throw new \Exception("Can't build request");
     }