Fix join

[ahelal]

Fixes #494

[tgross]

With fresh eyes the original line here looks questionable to me and I'm not sure what it's supposed to be getting us. Couldn't we do?:

func (f *MultiFlag) Set(value string) error {
 	if f.Len() == 0 {
 		f.Values = make(map[string]string, 1)
 	}
	pair := strings.SplitN(value, "=", 2)
	if len(pair) < 2 {
		return fmt.Errorf("flag value '%v' was not in the format 'key=val'", value)
	}
	f.Values[pair[0]] = pair[1]
	return nil
}

Do we have an example where the original line does something we need? It'd be nice to have a unit test for this.

[ahelal]

Hi @tgross,

I update the PR. I attempted to add a test, but was not sure I am in the right direction.
I wanted to check for -putenv ENV_VALUE=PART1 and -putenv ENV_VALUEPART1 to cover all cases. I kind of have the urge to test Set directly instead of using os.Args and then GetArgs()

But feeling lost somehow. So your input would be helpful.

[tgross]

I think this LGTM. Let's get it in!