Fixing for my slack login flow

Similar to https://github.com/CodeBuffet/Slekkel/pull/1 but slightly different approach.

At https://slack.com/signin I am prompted to enter a team name before moving forward (maybe slack has changed that since this was made?).
![signin](http://i.imgur.com/ea7mugn.png)

This change just prompts for you to enter that value and it will fill it for you before moving to the next page to enter the email address and password.