Documentation fix

[ldusan84]

The example from documentation doesn't work:

$issues = $client->api('orgs')->issues('KnpLabs', 'php-github-api', array('state' => 'open'));

It should be:

$issues = $client->api('organizations')->issues('KnpLabs', 'php-github-api', array('state' => 'open'));

[xabbuh]

👍 (well, the client could also be changed here in case people think using orgs is more convenient than organizations).