DevelopmentTools: fix type signature

While searching for `Pathname` usage in `extend/os/linux` as part of
fixing the `trash` type error, I noticed that `DevelopmentTools`
references `::Pathname` in the `locate` method signature but the type
signature for the `@locate` hash uses `Pathname` instead. This may
eventually error in a similar fashion, so this preemptively updates
the `@locate` type signature to use `::Pathname`.