Fix a failure of packman for --build_common_protos flag. (#51)
Fix a failure of packman for --build_common_protos flag. (#51)

The grpc plugin command-line is omitted when this flag is specified,
thus --grpc_out should also be omitted.
googleapis/packman,geigerj/packman,geigerj/packman,geigerj/packman,googleapis/packman,googleapis/packman,googleapis/packman,geigerj/packman