Thats is no package error, is that you failed to send data to device, do this to solve it:
images, labels = dataiter.next()
images, labels = images.to(device), labels.to(device) #ADD THIS LINE EVERY TIME YOU USE DATA

You will see that if you use CUDA to show NUMPY data you will have an error, DO NOT SEND to device the data that will use numpy!  (as numpy only works on cpu)
dataiter = iter(testloader)
images, labels = dataiter.next()
images, labels = images.to(device), labels.to(device) #sending here the data will make...

# print images
imshow(torchvision.utils.make_grid(images))             #THIS FAIL...numpy cpu...
print('GroundTruth: ', ' '.join('%5s' % classes[labels[j]] for j in range(4)))

TO MAKE ALL WORK ONLY SEND THEM BEFORE OUTPUT :
inputs, labels = inputs.to(device), labels.to(device)
outputs = net(inputs)
loss = criterion(outputs, labels)

#and on:

with torch.no_grad():
    for data in testloader:
        images, labels = data
        images, labels = images.to(device), labels.to(device) #here you go
        outputs = net(images)