Update getrandom requirement from 0.2 to 0.3

Updates the requirements on [getrandom](https://github.com/rust-random/getrandom) to permit the latest version.
- [Release notes](https://github.com/rust-random/getrandom/releases)
- [Changelog](https://github.com/rust-random/getrandom/blob/master/CHANGELOG.md)
- [Commits](rust-random/getrandom@v0.2.0...v0.3.4)

---
updated-dependencies:
- dependency-name: getrandom
  dependency-version: 0.3.4
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -34,7 +34,7 @@ ed25519-dalek = { version = "2.1.1", default-features = false, features = [
     "fast",
 ] }
 # Explicit dependency so we can pass the wasm-bindgen flag to it
-getrandom = { version = "0.2", optional = true }
+getrandom = { version = "0.3", optional = true }
 gridiron = "0.10"
 hex = "0.4"
 lazy_static = "1.4"