* gnu/packages/wm.scm (polybar): Update to 3.6.3.
[phases]: Add patch-config-path for polybar to find its default configuration
file in the store.
[inputs]: Add libuv, required to build polybar.
[native-inputs]: Remove python-2, no longer needed.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>