This amends the 'Use with Node' section to include the NodeJS error callback within the current optimization code example.
Document NodeJS error callback
Thanks for this contribution! I just had to find this out the hard way, as my build script was bailing with no output, and guessed that there might be an undocumented third parameter to optimize(). Was about to add it to the docs when I found this pull request. :)
Merged and applied to site. Thanks @toolness for pinging on this ticket, I wanted to merge earlier, but was heading out for vacation and it slipped through my task list.