Rename the 'name' to 'cognito_idp' (Use underscore instead of hyphen), easier connect with Rails/Devise

[ash-r1]

I'm using this gem with devise-omniauthable on Ruby on Rails. It implicitly uses its name option field in rails routing.

I have to configure with like below:

config.omniauth :cognito_idp,
  name: :cognito_idp,
  # other options

I know it's not bad of omniauth-cognito-idp, it's just a compatibility issue. They can also fix this issue.
But it might not cause any problem for Sinatra users, also I believe I achieve benefits for Rails users, please consider this change.