Update README to correct lists/member-info example.

To pass emails to the `lists/member-info` API call, the required key is `:emails` and not `:email_addresses`. See documentation here:

http://apidocs.mailchimp.com/api/2.0/lists/member-info.php
Merge pull request #55 from hoffm/patch-1

Update README to correct lists/member-info example.