Update version to 3.21.4

Adopt protobuf's .bazelrc to simplify cross-compilation

Merge pull request #144 from dibenede/prepare-release

Bump version to 3.21.2

Merge pull request #140 from dibenede/release-bugs

Fix typos in asserts and add LICENSE-asserts.md to package.json

Merge pull request #123 from dibenede/main

Update package-lock.json for version bump to v3.21.0