Update homepage field

Author: jmid

packages/conf-gtk3/conf-gtk3.18/opam

@@ -2,7 +2,7 @@ opam-version: "2.0"
 maintainer: "[email protected]"
 authors: "The GTK Toolkit"
 license: "LGPL-2.1-or-later"
-homepage: "https://developer.gnome.org/"
+homepage: "https://www.gtk.org/"
 bug-reports: "https://github.com/garrigue/lablgtk/issues"
 build: [
   ["pkgconf" "--personality=i686-w64-mingw32" "--print-errors" "--exists" "gtk+-3.0"] {os = "win32" & os-distribution = "cygwin" & host-arch-x86_32:installed}