[gtk/wip/ebassi/constraint-layout] Add gtkconstraintguide.h to the public headers

[Emmanuele Bassi <ebassi src gnome org>]

commit 7990b24287e355a54a029e793cd6f0ecdc272dfa
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Jul 1 01:12:25 2019 +0100

    Add gtkconstraintguide.h to the public headers
    
    It needs to be introspected and installed.

 gtk/meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/gtk/meson.build b/gtk/meson.build
index 696cbc5e29..428e1e49ab 100644
--- a/gtk/meson.build
+++ b/gtk/meson.build
@@ -465,6 +465,7 @@ gtk_public_headers = files([
   'gtkcolorutils.h',
   'gtkcombobox.h',
   'gtkcomboboxtext.h',
+  'gtkconstraintguide.h',
   'gtkconstraintlayout.h',
   'gtkconstraint.h',
   'gtkcontainer.h',