Fix simulator builds by adding +nightly

[garethknowles]

Adding +nightly to simulator builds seems to fix pd-rs/crank/issues/57

[boozook]

Thanks! 👍 But what if user hasn't rustup, but just nightly toolchain? This for example.

[paulyoung]

I don’t use rustup and adding +nightly causes errors for me.

It would be great if this could do something like check for the presence of rustup or be configured via an environment variable.

[boozook]

Rustup existence can be determined by env var, yes. Example.

[boozook]

Maybe just call crank so cargo +nightly crank? I'm not sure now, but if there cargo executable determined by CARGO env, it could fix this. 🤷🏻‍♂️