React Router v5

もともと4.4としてリリースしようとしていたが、react-router-domがreact-routerに依存していたらしい（not peer dependency）

But there was one case that we hadn't considered, which is that technically react-router-dom version 4.3.x could depend on react-router version 4.4, which they can't because of the changes to how we're using our internal context API. So although there were no public API breakages between 4.3.x and 4.4.0, there was a chance that some people could install 2 mismatched versions. What made this even trickier is that nobody noticed this bug until 4.4 was out of beta, because there was no chance you'd get a 4.4 beta installed alonside react-router-dom 4.3.x.