Replacing </form> with </div>

Thanks for teaching this course at JSConf! I finished up the exercises and found a few small things that needed to be fixed. I'm sending a pull request for each so you can review them individually.

This one fixes the closing element of .chat-form-wrapper in the exercise steps (sorry there are some white space fixes in there too, I have Sublime Text setup to trim trailing white space whenever I save a file)