message: Fix isort issue
diff: from concurrent import futures
  -import pytest
  import grpc
  +import pytest
  -from xain.grpc import helloworld_pb2_grpc, helloworld_pb2
  +from xain.grpc import helloworld_pb2, helloworld_pb2_grpc
  from xain.grpc.greeter_server import Greeter
  +
  @pytest.fixture
  def greeter_server():
  server = grpc.server(futures.ThreadPoolExecutor(max_workers=1))
  