set content-type application/json in contruct response

Author: harryolx

src/Response.php

@@ -16,11 +16,12 @@
 use PhpRestfulApiResponse\Contracts\PhpRestfulApiResponse;
 use Zend\Diactoros\MessageTrait;
 use InvalidArgumentException;
+use Zend\Diactoros\Response\InjectContentTypeTrait;
 use Zend\Diactoros\Response\JsonResponse;
 
 class Response implements PhpRestfulApiResponse
 {
-    use MessageTrait;
+    use MessageTrait, InjectContentTypeTrait;
 
     const MIN_STATUS_CODE_VALUE = 100;
     const MAX_STATUS_CODE_VALUE = 599;
@@ -131,6 +132,7 @@ public function __construct($body = 'php://memory', int $status = 200, $errorCod
         $this->setStatusCode($status);
         $this->setErrorCode($errorCode);
         $this->stream = $this->getStream($body, 'wb+');
+        $headers = $this->injectContentType('application/json', $headers);
         $this->setHeaders($headers);
     }
 
@@ -178,7 +180,6 @@ public function withArray($data, $code = 200, array $headers = [])
         $new = clone $this;
         $new->setStatusCode($code);
         $new->getBody()->write($this->jsonEncode($data));
-        $new = $new->withHeader('Content-Type', 'application/json');
         $new->headers = array_merge($new->headers, $headers);
         return $new;
     }
@@ -262,7 +263,6 @@ public function withError($message, int $statusCode, $errorCode = null, array $h
                 ]
             )
         );
-        $new = $new->withHeader('Content-Type', 'application/json');
         $new->headers = array_merge($new->headers, $headers);
         return $new;
     }