Cargo build panics

[badosu]

Upgrading envelope version should solve this as RustAudio/envelope#19 was merged and 0.8.1 was released.

When compiling with upgraded envelope I receive this error:

src/envelope.rs:28:10: 28:26 error: wrong number of type arguments: expected 0, found 1 [E0244]
src/envelope.rs:28 impl<'a> Trait<'a, Point> for Envelope {
                            ^~~~~~~~~~~~~~~~
src/envelope.rs:28:10: 28:26 help: run `rustc --explain E0244` to see a detailed explanation
error: aborting due to previous error
error: Could not compile `synth`.

I'd like to help doing this but I don't know anything about rust yet, I just wanted to run the example.

If you offer some guidance I may be able to try, though.