Add "True" to truthy value

[lihan]

Refer to this line, https://github.com/rconradharris/envparse/blob/master/envparse.py#L54

Can we have "True" as truthy value? It's python's format. If yes, I could do a PR.

Cheers

[maxandron]

It is unnecessary, the value is lowered: https://github.com/rconradharris/envparse/blob/master/envparse.py#L129