`config.cache` is not maintaining sort order of `dict`s

[BVMiko]

I'm running into an issue where I'm losing the sort order of a dict object when storing it with the config.cache:

    request.config.cache.set('foo', {'b':1,'a':2})
    print(request.config.cache.get('foo', None))

Returns:

{'a': 2, 'b': 1}

This issue is caused by the sort_keys parameter here:

pytest/src/_pytest/cacheprovider.py

Line 196 in 5fc7b21

data = json.dumps(value, indent=2, sort_keys=True)

I'm assuming this was written with Python 2.x in mind, but now that Python 3.x dict is sorted this is causing an issue. Could this be removed so that sort order is maintained?

[nicoddemus]

I think that would be fine, what do you think @RonnyPfannschmidt ?

[RonnyPfannschmidt]

This reminds me of a certain xkcd

It's fine to drop it i think

[nicoddemus]

@BVMiko would you like to contribute that change?