window: Use new xkbcommon include path

xkbcommon in current git has moved its include files.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/clients/window.h b/clients/window.h
index fd6e57b..301c86e 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -23,7 +23,7 @@
 #ifndef _WINDOW_H_
 #define _WINDOW_H_
 
-#include <X11/extensions/XKBcommon.h>
+#include <xkbcommon/xkbcommon.h>
 #include <glib.h>
 #include <wayland-client.h>
 #include <cairo.h>