[gtkmm] Gdk::DrawingContext: Include gdkmm/value_cairo.h

[Kjell Ahlstedt <kjellahl src gnome org>]

commit c66fde70e4863ac7f192e496e4bcab6d613f391a
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Oct 16 15:16:56 2017 +0200

    Gdk::DrawingContext: Include gdkmm/value_cairo.h

 gdk/src/drawingcontext.hg |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/gdk/src/drawingcontext.hg b/gdk/src/drawingcontext.hg
index 0ff89e3..3fc1b5f 100644
--- a/gdk/src/drawingcontext.hg
+++ b/gdk/src/drawingcontext.hg
@@ -17,6 +17,7 @@
 #include <glibmm/object.h>
 #include <cairomm/context.h>
 #include <cairomm/region.h>
+#include <gdkmm/value_cairo.h>
 
 _DEFS(gdkmm,gdk)
 _PINCLUDE(glibmm/private/object_p.h)