[gtk/matthiasc/for-master] docs: Fix a heading gotcha

[Matthias Clasen <matthiasc src gnome org>]

commit 880468f5a389f31aa5fa3d21223c03c44f471028
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jan 14 08:13:34 2021 -0500

    docs: Fix a heading gotcha
    
    One of the many migration guide sections was too
    prominent.

 docs/reference/gtk/migrating-3to4.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/docs/reference/gtk/migrating-3to4.md b/docs/reference/gtk/migrating-3to4.md
index 9942b46048..3d2fa1638b 100644
--- a/docs/reference/gtk/migrating-3to4.md
+++ b/docs/reference/gtk/migrating-3to4.md
@@ -522,7 +522,7 @@ option. You should always review the resulting changes.
 The <requires> tag now supports for the 'lib' attribute the
 'gtk' value only, instead of the 'gtk+' one previously.
 
-## Adapt to GtkBuilder API changes
+### Adapt to GtkBuilder API changes
 
 gtk_builder_connect_signals() no longer exists. Instead, signals are
 always connected automatically. If you need to add user data to your