[gtk+] MenuButton: Document the correct no-direction icon

[Daniel Boles <dboles src gnome org>]

commit 77b75bdab1d002da823011b3ae08e15cecb40da6
Author: Daniel Boles <dboles src gnome org>
Date:   Sun Oct 8 21:07:55 2017 +0100

    MenuButton: Document the correct no-direction icon
    
    Document open-menu-symbolic, which we use, not view-context-menu, which
    does not exist.

 gtk/gtkmenubutton.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gtk/gtkmenubutton.c b/gtk/gtkmenubutton.c
index 110c7b5..3a7e9b3 100644
--- a/gtk/gtkmenubutton.c
+++ b/gtk/gtkmenubutton.c
@@ -31,7 +31,7 @@
  * can hold almost any other standard #GtkWidget. The most commonly used
  * child is #GtkImage. If no widget is explicitely added to the #GtkMenuButton,
  * a #GtkImage is automatically created, using an arrow image oriented
- * according to #GtkMenuButton:direction or the generic "view-context-menu"
+ * according to #GtkMenuButton:direction or the generic “open-menu-symbolic”
  * icon if the direction is not set.
  *
  * The positioning of the popup is determined by the #GtkMenuButton:direction