Fix class naming calls

modules/invoice/classes/Invoice.php

@@ -93,7 +93,7 @@ SELECT i.id AS iid,i.due_date AS due FROM ab_invoice i,ab_invoice_item ii WHERE
 	 * Generate a PDF invoice
 	 */
 	public function pdf() {
-		$invoice_class = sprintf('Invoice_TCPDF_%s',ucfirst(Kohana::$config->load('invoice')->driver));
+		$invoice_class = Kohana::classname('Invoice_TCPDF_'.Kohana::$config->load('invoice')->driver);
 
 		$pdf = new $invoice_class($this->io);
 

modules/invoice/classes/Invoice/Tcpdf/Default.php

@@ -9,7 +9,7 @@
  * @copyright  (c) 2009-2013 Open Source Billing
  * @license    http://dev.osbill.net/license.html
  */
-class Invoice_TCPDF_Default extends Invoice_TCPDF {
+class Invoice_TCPDF_Default extends Invoice_Tcpdf {
 	// Current line being printed
 	public $sum_y = 0;