Emoji with dashes unsupported

[sj26]

There's a report in the emojis repo that :amazon-cogito: isn't recognised: buildkite/emojis#252

I believe it's because of this emoji regexp:

cli/local/emoji.go

Line 28 in e635a7d

var emojiRegexp = regexp.MustCompile(`:\w+:`)

\w does not include - (see the re2 docs) so it isn't matching.