py36+: use new NamedTuple syntax

[asottile]

See #7808

this one is slightly controversial, though I expect almost zero usage of 3.6.0

[bluetech]

If it's just for this I think it's probably not worth the hassle of the "3.6 but not 3.6.0" subtlety? We did endure 3.5.{0,1} which were much worse than this...

[asottile]

If it's just for this I think it's probably not worth the hassle of the "3.6 but not 3.6.0" subtlety? We did endure 3.5.{0,1} which were much worse than this...

there's also NoReturn in 3.6.2 but yeah this is pretty subtle. for what it's worth pre-commit does 3.6.1+ and there hasn't been any complaints thus far

[nicoddemus]

I see your point @asottile but I agree with @bluetech, I would prefer to avoid having to special case, and this case doesn't really buy us much.

However I think we can mark the code so it is clear that's only 3.6.0:

if sys.version_info[:3] == (3, 6, 0):
    # In 3.6.0 NamedTuples, ...
    class _ParameterSet(
        NamedTuple(
            "ParameterSet",
            [
                ("values", Sequence[Union[object, NotSetType]]),
                ("marks", Collection[Union["MarkDecorator", "Mark"]]),
                ("id", Optional[str]),
            ],
        )
    ):
    pass
else:    
    class _ParameterSet(NamedTuple):
        values: Sequence[Union[object, NotSetType]]
        marks: Collection[Union["MarkDecorator", "Mark"]]
        id: Optional[str]


class ParameterSet(_ParameterSet):
    ...

This helps finding the code when we drop 3.6.