SwiftLint2

Use `cp -Rf` instead of `cp -rf` in Makefile

`-r` option of `cp` copies symbolic links as normal files.
As the result of that, SwiftLintFramework.framework that distributed by Homebrew contains a lot of duplicated files inside that.
`-R` option copies symbolic links as symbolic links.

On my testing, this fix reduces the size of swiftlint-0.4.0.el_capitan.bottle.tar.gz from 17.2MB to 4.3MB.