Rust rand and slice compile error

I have some problems with my Rust program. I'm trying to create a vector with the numbers 48 to 57 and then randomly shuffle it. I'm running into the following errors

src/main.rs:7:26: 7:51 error: the type of this value must be known in this context
src/main.rs:7         let &mut slice = secret_num.as_mut_slice();
                                        ^~~~~~~~~~~~~~~~~~~~~~~~~
src/main.rs:9:13: 9:20 error: no method named `shuffle` found for type `rand::ThreadRng` in the current scope
src/main.rs:9         rng.shuffle(&mut slice);
                        ^~~~~~~

Here's the code:

extern crate rand;

fn main() {
    //Main game loop
    loop{
        let mut secret_num = (48..58).collect();
        let &mut slice = secret_num.as_mut_slice();
        let mut rng = rand::thread_rng();
        rng.shuffle(&mut slice);                                            
        println!("{:?}", secret_num);
        break;
    }
    println!("Hello, world!");
}