Slack gotcha: Nicknames starting with `@`

If we specify username nick with mention prefix @ (e.g. +1 @voter101). PlusOne bot will convert that nick to match name without prefixing @ character.

Unfortunatelly this operation isn't performed by simple string operation. Slack converts all nicknames in this format. It uses it's own user format looking like this:

• <@USLACKBOT> - unique ID for Slackbot
• <@U029FH1FH> - ID of some user from our Slack

We can hit hit Slack API to fetch information about user hidden behind given tag. We presume that user whose name doesn't begin with <@ is valid nickname and doesn't need hitting Slack API to decode.