useDefaultAuth logout hard coded header

[ExcelNet-Public]

logout = ->
      # Remove the given auth token from the user's account
      authToken = @request.headers['x-auth-token']

This needs to get the authToken by calling the user function if defined. We have an application that cannot adjust the headers (not ours, no source access) and wrote a custom user function to return the userId / token. However the code above breaks and causes a crash since that header does not exist if our application tries to logout.