deps: update fiat-crypto requirement from 0.1.11 to 0.2.1

Updates the requirements on [fiat-crypto](https://github.com/mit-plv/fiat-crypto) to permit the latest version.
- [Release notes](https://github.com/mit-plv/fiat-crypto/releases)
- [Commits](https://github.com/mit-plv/fiat-crypto/commits)

---
updated-dependencies:
- dependency-name: fiat-crypto
  dependency-type: direct:production
...

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

Cargo.toml

@@ -20,7 +20,7 @@ exclude = [
 [dependencies]
 subtle = { version = "^2.2.2", default-features = false }
 zeroize = { version = "1.1.0", default-features = false }
-fiat-crypto = {version = "0.1.11", default-features = false}
+fiat-crypto = {version = "0.2.1", default-features = false}
 getrandom = { version = "0.2.0", optional = true }
 ct-codecs = { version = "1.1.1", optional = true }