[gnome-calendar] source-dialog: add missing include

[Erick Pérez Castellanos <erickpc src gnome org>]

commit 1de622f4e034830f666fc0ce84339ce2f09fe7af
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Mon Feb 9 11:16:23 2015 -0200

    source-dialog: add missing include

 src/gcal-source-dialog.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/src/gcal-source-dialog.h b/src/gcal-source-dialog.h
index 732c9b1..c0b8cad 100644
--- a/src/gcal-source-dialog.h
+++ b/src/gcal-source-dialog.h
@@ -22,6 +22,8 @@
 
 #include <glib-object.h>
 
+#include <gtk/gtk.h>
+
 G_BEGIN_DECLS
 
 #define GCAL_TYPE_SOURCE_DIALOG (gcal_source_dialog_get_type())