completed_at was renamed to paid_at

Author: shesek

templates/completed.php

@@ -3,7 +3,7 @@
 <h2>Payment completed successfully</h2>
 <ul class="order_details">
   <li>
-    Payment completed at: <strong><?php echo date('r', $invoice->completed_at) ?></strong>
+    Payment completed at: <strong><?php echo date('r', $invoice->paid_at) ?></strong>
   </li>
   <li>
     Lightning rhash: <strong><?php echo $invoice->rhash ?></strong>