package/cog: bump to version 0.3.1

Update the package to version 0.3.1, which includes build improvements.
In particular, it now uses wayland-scanner to generate Wayland protocol
code instead of shipping pre-generated files.

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>