Support wasm target

[kazk]

Resolves #6

[kazk]

To use with wasm-pack, getrandom's js feature must be enabled. The feature makes getrandom assume that you are building for an environment containing JavaScript.

# `getrandom` is a dependency of `rand` which is in turn a dependency of `xid`.
# Enable `js` feature to support `wasm32-unknown-unknown` target used by `wasm-pack`.
# Makes `getrandom` assume that you are building for an environment containing JavaScript.
# See https://docs.rs/getrandom/latest/getrandom/#webassembly-support
getrandom = { version = "0.2.7", features = ["js"] }