Add feature to support id and name in HUBOT_AUTH_ADMIN

[sebastiandero]

I think the above mentioned feature would make hubot-auth alot more intuitive. The feature would be quite simple to implement aswell, instead of using this:

class Auth
    isAdmin: (user) ->
      user.id.toString() in admins

using this would provide username support:

class Auth
    isAdmin: (user) ->
      (user.id.toString() in admins) or (user.name.toString() in admins)

Please think about it, i will provide and link a pull request aswell

[sebastiandero]

Pullrequest for the feature: #49

[sebastiandero]

Support is insecure since one can spoof their name on some adapters