Support 3.8 with tests fix

[uburuntu]

Hi!

I want to use Fire in project with Python 3.8, so I think library should be officially supported for 3.8.

I added travis run for 3.8 and one test testInitRequiresFlagSyntaxSubclassNamedTuple got failed: link.

Investigation showed that now namedtuple attributes of type collections._tuplegetter since 3.8, not property: link, commit:

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So I added backward compatibility check in MemberVisible function.

One not solved trouble: pytype does not support 3.8 (google/pytype#587) -- https://travis-ci.org/github/uburuntu/python-fire, but I can add check in travis.yml to skip it currently.

[dbieber]

Thanks 🙏
Skipping pytype for 3.8 is fine.

[uburuntu]

Done 🙂

Build status: https://travis-ci.org/github/uburuntu/python-fire

[uburuntu]

Now with pytype 🙃

Build status: https://travis-ci.org/github/uburuntu/python-fire

[ssbarnea]

This is going to show us how fast the project is going to adapt. Based on #139 which is almost two years old, I would say that a lot. I am keeping an eye on Fire but I will avoid it for the moment on my own projects.

[dbieber]

Thanks for the update @uburuntu and for the review @ssbarnea.
This LGTM.

Merge will happen within the next 2-3 weeks, I expect.

[dbieber]

Merged in 457b156