Minor bug in the set_dataset_info of loader_pyg.py module

[vivek-vijayan-k]

torch_geometric.data.keys() is a method. Since the code mentioned above tries to iterate through the method instead of calling the method and iterate through results, I was getting TypeError: 'method' object is not iterable when I try to run_single_pyg.sh Please modify the code to resolve this issue. Since this is minor bug and I'm still learning this wonderful library, I thought it's worth pointing out.