Correct Enterprise API documentation (issue KnpLabs#636)

Author: Jacob Truman

doc/enterprise.md

@@ -12,10 +12,8 @@ In order to configure the client to point to a GitHub Enterprise installation, d
 // This file is generated by Composer
 require_once 'vendor/autoload.php';
 
-$client = new \Github\Client();
-
-// Set the URL of your GitHub Enterprise installation
-$client->setEnterpriseUrl('https://ghe.host');
+// Specify the URL of your GitHub Enterprise installation on client initialization
+$client = new \Github\Client(null, null, 'https://ghe.host');
 
 // Use the client as you would ordinarily
 $repositories = $client->api('user')->repositories('ornicar');