[gtk] README: Fix Gdk doc website link

[Carlos Soriano <csoriano src gnome org>]

commit 3e6a47308254fa685430e34c9cd7505e02b4aa33
Author: Carlos Soriano <csoriano1618 gmail com>
Date:   Sun Aug 5 21:59:27 2018 +0000

    README: Fix Gdk doc website link

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index aa13e92f9c..689042ad39 100644
--- a/README.md
+++ b/README.md
@@ -33,7 +33,7 @@ Information about mailing lists can be found at
 
 Nightly documentation can be found at
   - Gtk: https://gnome.pages.gitlab.gnome.org/gtk/gtk/
-  - Gdk: https://gnome.pages.gitlab.gnome.org/gtk/gtk/
+  - Gdk: https://gnome.pages.gitlab.gnome.org/gtk/gdk/
   - Gsk: https://gnome.pages.gitlab.gnome.org/gtk/gsk/
 
 Building and installing