Wrong parameter name calling model.cuda()

[zangxc]

Symptom:
Build failed on ubuntu 16.04, pytorch 0.3.1-py36_cuda8.0.61_cudnn7.0.5_2
Reason:
As stated here: https://pytorch.org/docs/master/nn.html
Parameter for cuda() function should be "device" instead of "device_id".
Suggested Fix:
Replace device_id with device on:
rlpytorch/model_interface.py line 98
rlpytorch/model_loader.py line 95