change the dzil phase to satisfy DZP::VerifyPhases

I was using ETHER's excellent VerifyPhases plugin and noticed this:

[@Apocalyptic/VerifyPhases] file has been added after file gathering phase: 'AUTHOR_PLEDGE' (content added by @Apocalyptic/Covenant (Dist::Zilla::Plugin::Covenant line 51))

I investigated this and it was a simple fix! Thanks for looking into this :)