Support sinon 5

[westy92]

No description provided.

[kaiyoma]

I think this should be bumped up in priority because sinon 5.0.1 was just released. Now if I try to run the latest release of both packages, I get yarn check errors.

[voxpelli]

What about not limiting the upper version but rather specify the minimum version of Sinon that is required? And only limit it when shown that a version can't be compatible with both an older and a newer version?

• some docs on which versions sinon-chai is tested with.

This should also extend the test matrix: https://github.com/domenic/sinon-chai/blob/master/.travis.yml#L8