0.8.1 fails to compile for no-std

[schungx]

The added feature of getrandom/js is breaking no-std builds by pulling in wasm-bindgen (for no reason).

EDIT: rust-lang/cargo#4866 and rust-lang/cargo#1197 document the fact that target-specific features are not supported. All features are merged regardless of target.

This is an issue in addition to #140.

[schungx]

I strong concur with #140 that the best solution is to add a js feature which turns on getrandom/js.

JavaScript interop is really an external feature outside of core target architecture and O/S, so it is reasonable to assume that it should be specifically specified.

Assuming the existence of JavaScript for all wasm and no-std targets is simply wrong; since not all warm runs on a browser, and no-std most likely doesn't have JavaScript around.

[tkaitchuck]

Fixed.