bug: custom `help_trigger()` not applied in `from_env()` err

[ver-nyan]

Hi, i noticed custom help_trigger() is not applied in from_env() and always defaults to --help. If not using --help, you could end up with:

Unrecognized argument: --help

Run foo --help for more information.

The snippet in from_en():

argh/argh/src/lib.rs

Line 814 in 7184aab

eprintln!("{}\nRun {} --help for more information.", early_exit.output, cmd);

This isn't a big deal for me since I'm using my own entire help message anyways, but I just wanted to point this out.