added decimal format variable for invoice duration (#1037)

tests/Invoice/Renderer/DebugRenderer.php

@@ -80,6 +80,15 @@ class DebugRenderer implements RendererInterface
         return $seconds;
     }
 
+    /**
+     * @param mixed $seconds
+     * @return mixed
+     */
+    protected function getFormattedDecimalDuration($seconds)
+    {
+        return $seconds;
+    }
+
     /**
      * Render the given InvoiceDocument with the data from the InvoiceModel into a stupid array for testing only.
      *