Bump @grpc/grpc-js from 1.1.7 to 1.1.8

Bumps [@grpc/grpc-js](https://github.com/grpc/grpc-node) from 1.1.7 to 1.1.8.
- [Release notes](https://github.com/grpc/grpc-node/releases)
- [Commits](https://github.com/grpc/grpc-node/commits)

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