Fix GPU run for PyTorch Ignite and Lightning examples.

[arisliang]

Motivation

The pytorch ignite and lightning example failed to run using GPU.

Description of the changes

This PR fix the run with GPU.

[toshihikoyanase]

Thank you for your PR! The change looks good to me.
Please check two small comments.

[toshihikoyanase]

@keisuke-umezawa @hvy @HideakiImamura
I think we had a coding style convention to put two blank lines after library imports, but I cannot find it in the current guide. Can we accept this change?

[hvy]

Oh, I did not know that. We have existing code where there's a single blank line, e.g. similar to this case where variables are declared (e.g. logger objects) or conditions using try_import. I thought that the "two blank lines rule" stemmed from PEP-8 https://www.python.org/dev/peps/pep-0008/#blank-lines and that it's okay as long as we follow

Surround top-level function and class definitions with two blank lines.

(But I do think that it's confusing having the style checkers (black, hacking) accept either here.)

[toshihikoyanase]

@hvy Thank you for your comment.

I thought that the "two blank lines rule" stemmed from PEP-8 https://www.python.org/dev/peps/pep-0008/#blank-lines

I understand. I'd like to accept this change according to PEP-8.

[toshihikoyanase]

Thank you for your update. LGTM.!

[hvy]

Thanks for the fixes, changes LGTM!

[hvy]

Let me slightly modify the title to match the release note format https://github.com/optuna/optuna/blob/master/CONTRIBUTING.md#title.