fix resp body

Author: Jamie Hannaford

src/Common/Error/Builder.php

@@ -73,7 +73,7 @@ private function linkIsValid($link)
         return $resp->getStatusCode() < 400;
     }
 
-    private function str(MessageInterface $message)
+    public function str(MessageInterface $message)
     {
         if ($message instanceof RequestInterface) {
             $msg = trim($message->getMethod() . ' '

tests/unit/Common/Error/BuilderTest.php

@@ -35,8 +35,8 @@ public function test_it_builds_http_errors()
         $request = new Request('POST', '/servers');
         $response = new Response(400, [], stream_for('Invalid parameters'));
 
-        $requestStr = trim(str($request));
-        $responseStr = trim(str($response));
+        $requestStr = trim($this->builder->str($request));
+        $responseStr = trim($this->builder->str($response));
 
         $errorMessage = <<<EOT
 HTTP Error