explicitly define prereqs

Path::Class must be at least 0.35 for copy_to(), which causes the
following error:

    Can't locate object method "copy_to" via package "Path::Class::File"
    at lib/Dist/Zilla/Plugin/ChangelogFromGit/CPAN/Changes.pm line 180.

It's also a good idea to explicitly list the modules depended on, in case other expected modules change their prereqs.