message: Update pipeline_client.py
  fix string_data to str_data
diff: @@ -108,7 +108,7 @@ class PipelineClient(object):
  one_tensor.name = key
  if isinstance(value, str):
  - one_tensor.string_data.add(value)
  + one_tensor.str_data.append(value)
  one_tensor.elem_type = 12 #12 => string in proto
  continue
  