Docs incorrect about ArgGroups in YAML

[laishulu]

with the following yaml file, when I invoke myapp without any arguments, it just passes.
But according to the spec, at least one of base and delta should be presented.
Also, I don't find anything about the arg group when I invoke myapp help

name: myapp
version: 0.1
about: myapp
global_settings:
    - ColoredHelp
args:
    - base:
        long: base
        value_name: BASE
        help: Base
        takes_value: true
        display_order: 2
    - delta:
        long: delta
        value_name: DELTA
        help: delta
        takes_value: true
        display_order: 3
arg_groups:
    - test:
        args:
            - base
            - delta
        required: true

[laishulu]

Oh, I found if use goups instead of arg_groups, then it works.
but the document and examples (https://github.com/kbknapp/clap-rs/blob/master/examples/17_yaml.yml#L87) should be updated.

[kbknapp]

Ah thank you for pointing this out! This was a change between v1 to v2.

[kbknapp]

#603 fixes this