Add Content-Type: application/json header to API responses

src/Webservice/Renderer.php

@@ -25,6 +25,7 @@ class Renderer
     {
         header(sprintf('HTTP/1.0 %s %s', $status, self::$statusMessages[$status]));
         header("Access-Control-Allow-Origin: *");
+        header("Content-Type: application/json; charset=utf-8");
 
         ob_clean();
         flush();