MAINT: Upgrade pytest again

[jkseppan]

See pytest-dev/pytest#5358

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[timhoffm]

Are we fine with bumping pytest, or should we simply leave pytest!=4.6.0 in?

[QuLogic]

Yes, I don't understand why the minimum needs to be bumped here either.

[jkseppan]

I don't see why not use the latest pytest: it's not a requirement for users but what we run ourselves in CI. But I suppose specifying !=4.6.0 is effectively the same, just more complex for the people who will look at the files in the future.

[jkseppan]

The tests pass now, and it seems that both Travis and Appveyor are using pytest 4.6.1.