Remove duplicate Content-type header (#4026)

The Grafana plugin is broken, because the generated request has two http header (Content-type and Content-Type). The later one, it the correct header and its added by \Deployer\Utility\Httpie::jsonBody

Author: webflo

contrib/grafana.php

@@ -61,7 +61,6 @@
 
     Httpie::post($config['url'])
         ->header('Authorization', 'Bearer ' . $config['token'])
-        ->header('Content-type', 'application/json')
         ->jsonBody($params)
         ->send();
 });