Bump browserslist from 4.16.0 to 4.21.3 in /examples/grpc-web (#70)

Bumps [browserslist](https://github.com/browserslist/browserslist) from 4.16.0 to 4.21.3.
- [Release notes](https://github.com/browserslist/browserslist/releases)
- [Changelog](https://github.com/browserslist/browserslist/blob/main/CHANGELOG.md)
- [Commits](browserslist/browserslist@4.16.0...4.21.3)

---
updated-dependencies:
- dependency-name: browserslist
  dependency-type: indirect
...

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

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

Author: dependabot[bot]