refactor(OrbitClient): Update Forge Environment for Stage (#25)

refator(OrbitClient): Update Forge Environment for Stage

## Change
- updates headers for Orbit Client to have `forge-free` in stage environment

## JIRA
https://jira.dev.bbc.co.uk/browse/DATCAP-80

src/OrbitClient.php

@@ -201,6 +201,7 @@ private function getRequestHeaders(array $options)
         }
         if ($this->options['env'] === 'stage') {
             $headers['x-forge-environment'] = 'stage';
+            empty($headers['X-Feature']) ? $headers['X-Feature'] = 'forge-free' : $headers['X-Feature'] .= ', forge-free';
         }
         return $headers;
     }