Log Message:
Update to 6.006

Upstream changes:
6.006     2016-07-04 10:56:36-04:00 America/New_York
        - add some documentation to Dist::Zilla::App::Tester (thanks, Alberto
          Simç¹­es!)
        - optimizations to regex munging (thanks, Olivier Mengu矇!)
        - add x_serialization_backend to META.* files (thanks, Karen
          Etheridge!)
        - metadata plugins are called before metadata defaults are built
          (thanks, Karen Etheridge!)
        - don't use ExtraTests plugin, but if you do, its generated test files
          are a bit faster when unused