message: Fix black issues
diff: from concurrent import futures
  -import grpc
  import pytest
  +import grpc
  -from xain.grpc import helloworld_pb2, helloworld_pb2_grpc
  +from xain.grpc import helloworld_pb2_grpc, helloworld_pb2
  from xain.grpc.greeter_server import Greeter
  