Now that there are two different versions of rake, please make sure that it is possible to see the version of the old `rake` attribute in `all-packages.nix`, too. The common approach is to have an attribute `rakexyz` for every version x.y.z, plus an attribute `rake` that just refers to the version of rake we use by default. Also, the file `./development/ruby-modules/rake/default.nix` should probably be renamed so that its filename is consistent with the newly added `10.nix` expression.