Bump crypto-bigint from 0.2.7 to 0.2.8 (RustCrypto#35)

Bumps [crypto-bigint](https://github.com/RustCrypto/crypto-bigint) from 0.2.7 to 0.2.8.
- [Release notes](https://github.com/RustCrypto/crypto-bigint/releases)
- [Changelog](https://github.com/RustCrypto/crypto-bigint/blob/master/CHANGELOG.md)
- [Commits](https://github.com/RustCrypto/crypto-bigint/commits/v0.2.8)

---
updated-dependencies:
- dependency-name: crypto-bigint
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>