[gtkmm] Box: pack_end(): Don't call a pack_start() method.

[Murray Cumming <murrayc src gnome org>]

commit 74a915b3289a34fc88eed35f926d7f88f9303c10
Author: Murray Cumming <murrayc murrayc com>
Date:   Fri Jun 23 08:10:53 2017 +0200

    Box: pack_end(): Don't call a pack_start() method.
    
    This was a copy/paste error.
    Bug #784118 (Marc Micalizzi)

 gtk/src/box.ccg |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/src/box.ccg b/gtk/src/box.ccg
index 5226e90..48624eb 100644
--- a/gtk/src/box.ccg
+++ b/gtk/src/box.ccg
@@ -45,7 +45,7 @@ void Box::pack_end(Widget& child, PackOptions options)
 {
   // Avoid using our custom code in this case:
   if (options == PackOptions::SHRINK) {
-    return pack_start(child);
+    return pack_end(child);
   }
 
   const bool expand = (options == PackOptions::EXPAND_PADDING) || (options == PackOptions::EXPAND_WIDGET);