Update talk.html

I didn't try to run it and am not sure if I'm understanding it right
but I took a guess it might suppose to read append_circles().

I also couldn't get the talk to talk to display properly after cloning 
the repo because the reveal.js directory was empty. I tried
`git clone --recursive ...` but that gave me some error about
"No submodule mapping found in .gitmodules for path 'static/reveal.js'".
I'm not familiar with how this git setup is supposed to work so I 
ended up manually cloning reveal.js into the subdirectory which 
worked.