Updated sample code in README.md to prevent error '[MixpanelExport] You must implement the .done(json) method on the result of your API call!' when using the sample code provided.
Squashed commit of the following:

commit b72f3ca97691f6534ba99511aa6bbf609ee083ea
Author: Matthew Palmer <matt@palmer.im>
Date:   Sat Nov 2 09:14:07 2013 +1100

    Fix minor typo in README.md

commit b3b433b5ceca4f53d34881c915886b041db42fa5
Author: Matthew Palmer <matt@palmer.im>
Date:   Sat Nov 2 09:13:04 2013 +1100

    Delete .DS_Store
Merge pull request #1 from matthewpalmer/master

Updated sample code in README.md