ArgGroup yaml creation does not allow multiple option

[ZoeyR]

Affected Version of clap

2.20.1

Expected Behavior Summary

ArgGroup is created from Yaml

Actual Behavior Summary

Program errors out with
thread 'main' panicked at 'Unknown ArgGroup setting 'multiple' in YAML file for ArgGroup 'io'', C:\Users\<user>\.cargo\registry\src\github.com-1ecc6299db9ec823\clap-2.20.1\src\args\group.rs:493

Steps to Reproduce

create yaml file similar to the following

name: dungeon
version: "0.1.0"
author: Daniel Griffen <daniel@griffen.io>
args:
    - save:
        short: s
        long: save
        value_name: FILE
        min_values: 0
        max_values: 1
    - load:
        short: l
        long: load
        value_name: FILE
        min_values: 0
        max_values: 1
groups:
    - io:
        args: [save, load]
        multiple: true

Try and create matches object with

let yaml = load_yaml!("cli.yml");
let matches = App::from_yaml(yaml).get_matches();