[bug] inside createTask function in mandellib.js, generation is undefined

[sinwailam193]

Hi Beth,

I learned a lot from your books, thank you for you're doing. As I came across in one of your chapters for the html5 book, the function createTask in mandellib.js contains an undefined variable, "generation". I simply added a second parameter into the function and in mandel.js I passed in 'generation' into the createTask for the web worker.