updates API for random number generator in a range

there is an API update for generating a number in a range
http://static.rust-lang.org/doc/master/std/rand/trait.Rng.html#method.gen_integer_range

I'm using the following rust compiler:

rustc --version
rustc 0.8
host: x86_64-apple-darwin

Maybe the wording needs a bit of change since it removes one example (the abs one). 
Anyway I thought that it would be nice to have the book updated since I had to chase this "bug" for a while.