Fix build fail when xcb-util-xrm not installed

When this package is not installed, the struct randr type never gets fully
defined because randr.hpp never gets included. This causes the build to fail in
update_monitor_ref.

See issue mihirlad55/polybar-dwm-module#10.

src/modules/dwm.cpp

@@ -8,6 +8,7 @@
 #include "modules/meta/base.inl"
 #include "utils/env.hpp"
 #include "utils/file.hpp"
+#include "x11/extensions/randr.hpp"
 
 POLYBAR_NS