Cannot use UserApps

[C0D3-M4513R]

Eventhough that #266 and serenity's dependency pr are both merged I still cannot use this in my application using 1.12.4 of serenity and 0.6.1 of poise.

The example https://github.com/serenity-rs/poise/blob/current/examples/feature_showcase/user_apps.rs also doesn't work for me, because: Unknown field: install_context.

I also cannot just use a patch section or use the git version, because then nix will (my packaging system) will complain, that poise doesn't have a checksum. This effectively means that I cannot use User-Apps, whilst using nix to build my docker containers.