specify @ symbol or not when asking for Twitter handle

[kmugrage]

specify @ symbol or not when asking for Twitter handle

[mattstratton]

Yeah, as you can see in https://github.com/devopsdays/devopsdays-cli/blob/master/helpers/validate_field.go#L27-L31, we actually do not want the @ symbol.

There are a couple things we could do:

1. Make sure the prompt says "enter the twitter handle without the @ symbol"
   or
2. Allow it with or without, and then just strip it ourselves.

Option 2 seems best.

[kmugrage]

yeah, 2 seems best