Remove incorrect information about state param
Remove incorrect information about state param

Omniauth uses the state param for providing automatic CSRF protection, if you do try and pass a `?state=XXX` param it will effectively be clobbered internally by omniauth, and will not be echoed back during the callback phase. Example:

```
GET /auth/slack?state=123

...auth on Slack...

GET /auth/slack/callback?code=XXX&state=OMNIAUTH_CSRF_TOKEN
```
kmrshntr/omniauth-slack,horiaradu/omniauth-slack,omsl/omniauth-slack,gssbzn/omniauth-slack,jwright/omniauth-slack