[gnome-todo] manager: Avoid singleton instance being public

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 77ade02b113a855df112d8c592de3bdad0f1c94d
Author: Yi-Soo An <yisooan gmail com>
Date:   Fri Sep 14 12:41:13 2018 +0900

    manager: Avoid singleton instance being public
    
    without static, the instance could be accessed by other translation units.
    
    To fix it, add static keyword to be as private.

 src/engine/gtd-manager.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/engine/gtd-manager.c b/src/engine/gtd-manager.c
index 723b2b1..da387c8 100644
--- a/src/engine/gtd-manager.c
+++ b/src/engine/gtd-manager.c
@@ -70,7 +70,7 @@ struct _GtdManager
 G_DEFINE_TYPE (GtdManager, gtd_manager, GTD_TYPE_OBJECT)
 
 /* Singleton instance */
-GtdManager *gtd_manager_instance = NULL;
+static GtdManager *gtd_manager_instance = NULL;
 
 enum
 {