[gtk+] Install gtkcenterbox.h

[Matthias Clasen <matthiasc src gnome org>]

commit bffbfde10a7ade79eeca6a82dcf118fda85a6741
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Jun 5 21:09:30 2017 -0400

    Install gtkcenterbox.h

 gtk/Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gtk/Makefile.am b/gtk/Makefile.am
index 5c932b1..82c725f 100644
--- a/gtk/Makefile.am
+++ b/gtk/Makefile.am
@@ -164,6 +164,7 @@ gtk_public_h_sources =              \
        gtkcellrenderertext.h   \
        gtkcellrenderertoggle.h \
        gtkcellview.h           \
+       gtkcenterbox.h          \
        gtkcheckbutton.h        \
        gtkcheckmenuitem.h      \
        gtkclipboard.h          \