@babel/runtime should be a peerDependency instead of dependency

If `@babel/runtime` were set to be a `peerDependency` it would allow users of this library to choose which version of `@babel/runtime` to install. Our web app already uses multiple different versions of `@babel/runtime`. After installing `react-sortable-hoc`, we saw an increase of 2 KiB due to `@babel/runtime`. By forcing it to be a "dependency" and not "peerDependency", we end up duplicating code.