message: Update prepare_model.py
diff: @@ -16,7 +16,9 @@ import paddlehub as hub
  import paddle.fluid as fluid
  import sys
  import paddle_serving_client.io as serving_io
  +import paddle
  +paddle.enable_static()
  model_name = "bert_chinese_L-12_H-768_A-12"
  module = hub.Module(model_name)
  inputs, outputs, program = module.context(
  