`AttributeError: module 'torch_optimizer' has no attribute 'MAGRAD'`

I tired to follow the example of using MAGRAD optimizer 
```
  import torch_optimizer as optim
   optimizer = optim.MAGRAD(model.parameters(), lr=0.1)
   optimizer.zero_grad()
   loss_fn(model(input), target).backward()
   optimizer.step()
```
but got 
`AttributeError: module 'torch_optimizer' has no attribute 'MAGRAD'`