Improve detection of slack tokens

[byo]

Current regex for slack tokens seems to be to narrow to handle all slack tokens. I did check three leaked slack tokens (just search for xoxa or xoxp in all github issues), one of them obfuscated, others seem to be a correct ones which does not match the regex.

Also current regex does not match refresh tokens starting with xoxr (https://api.slack.com/docs/token-types).

[andrew-kline]

@dxa4481 hi - discovered this as well. The regex for slack tokens here https://github.com/l4yton/RegHex seems to be more inclusive.

[dxa4481]

Thanks for the reference, I'll update the regex

[dxa4481]

Added a few more letters in there (like reghex has) hopefully that covers them all, let me know what you think