[four-in-a-row] Fixes #10: fixed segfault

[Michael Catanzaro <mcatanzaro src gnome org>]

commit e157587501d89793a8c9d66dfeb2fdf4af737e4b
Author: Jacob Humphrey <jacob ryan humphrey gmail com>
Date:   Sun Dec 16 18:17:05 2018 -0600

    Fixes #10: fixed segfault

 src/prefs-box.vala | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/prefs-box.vala b/src/prefs-box.vala
index b6e5020..83c3407 100644
--- a/src/prefs-box.vala
+++ b/src/prefs-box.vala
@@ -36,6 +36,7 @@ class PrefsBox : Gtk.Dialog {
             title: _("Preferences"),
             destroy_with_parent: true);
         set_transient_for(parent);
+        this.application = parent.application;
         modal = true;
         border_width = 5;
         get_content_area().spacing = 2;