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.c b/clients/window.c
index 052fefb..7fc35d8 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -49,7 +49,7 @@
 #include <cairo-gl.h>
 #endif
 
-#include <X11/extensions/XKBcommon.h>
+#include <xkbcommon/xkbcommon.h>
 #include <X11/X.h>
 
 #include <linux/input.h>