AttributeError: 'tensorrt.tensorrt.Builder' object has no attribute 'max_workspace_size'

When I run the Usage demo

import torch
from torch2trt import torch2trt
from torchvision.models.alexnet import alexnet

# create some regular pytorch model...
model = alexnet(pretrained=True).eval().cuda()

# create example data
x = torch.ones((1, 3, 224, 224)).cuda()

# convert to TensorRT feeding sample data as input
model_trt = torch2trt(model, [x])

An error occurs:

AttributeError                            Traceback (most recent call last)
~/Documents/github/fast-reid/demo/convert2trt.py in <module>
----> 1 model_trt = torch2trt(model_alex, [x])

~/anaconda3/envs/detect2/lib/python3.6/site-packages/torch2trt-0.2.0-py3.6.egg/torch2trt/torch2trt.py in torch2trt(module, inputs, input_names, output_names, log_level, max_batch_size, fp16_mode, max_workspace_size, strict_type_constraints, keep_network, int8_mode, int8_calib_dataset, int8_calib_algorithm, int8_calib_batch_size, use_onnx, **kwargs)
    546             ctx.mark_outputs(outputs, output_names)
    547 
--> 548     builder.max_workspace_size = max_workspace_size
    549     builder.fp16_mode = fp16_mode
    550     builder.max_batch_size = max_batch_size

AttributeError: 'tensorrt.tensorrt.Builder' object has no attribute 'max_workspace_size'

What is the problem? Many thanks!