Update src/TestSuite/Constraint/Response/ContentType.php

Co-Authored-By: Edgaras Janušauskas <edgaras.janusauskas@gmail.com>

src/TestSuite/Constraint/Response/ContentType.php

@@ -43,6 +43,6 @@ class ContentType extends ResponseBase
      */
     public function toString()
     {
-        return 'was set as the Content-Type (`' . $this->response->getType() . '`)';
+        return 'is set as the Content-Type (`' . $this->response->getType() . '`)';
     }
 }