fix typo

Author: clarkeash

doc/repos.md

@@ -291,7 +291,7 @@ $repo = ResponseMediator::getContent($data);
 ### Get the milestones of a repository
 
 ```php
-milestones = $client->api('repo')->milestones('ornicar', 'php-github-api');
+$milestones = $client->api('repo')->milestones('ornicar', 'php-github-api');
 ```
 
 Returns a list of milestones.