jsonrpcserver package version changed to 4.2.0 (available at pypi repository) to avoid setup problems caused by old pip tool version

jsonrpcserver package version changed to 4.2.0 (available at pypi repository) to avoid setup problems related to referencing git commit (it was bad handled by pip version older than 18). In such case, git commit has been silently ignored and pip installed latest version available at PyPi (jsonrpsserver 5.0.2) what was wrong.