Ruby 2.5.0 Support

[Brandon High]

The specs fail with this error:

3) PathSpec#match_tree unix 
     Failure/Error:
       Find.find(root) do |path|
         relpath = Pathname.new(path).relative_path_from(rootpath).to_s
         relpath += '/' if File.directory? path
         if match(relpath)
           matching << path
         end
     
     NoMethodError:
       undefined method `children' for FakeFS::Dir:Class
     # ./lib/pathspec.rb:41:in `match_tree'
     # ./spec/unit/pathspec_spec.rb:191:in `block (4 levels) in <top (required)>'
     # ./spec/unit/pathspec_spec.rb:196:in `block (4 levels) in <top (required)>'