`Cask::Artifact::AbstractUninstall.uninstall_script` contains a
`which` call that uses a `Pathname` argument instead of a `String` and
this leads to a type error (`Parameter 'cmd': Expected type String,
got type Pathname with value...`). This resolves the error by calling
`#to_s` on the `executable_path` argument.
ba0bc88b3d