Cabal revisions of extra-1.6.15

Hackage metadata revisions edit the .cabal file after upload; each diff below is one revision.

 build-type:         Simple name:               extra version:            1.6.15+x-revision: 1 license:            BSD3 license-file:       LICENSE category:           Development     default-language: Haskell2010     hs-source-dirs: src     build-depends:-        base >= 4.8 && < 5,+        base >= 4.8 && < 4.15,         directory,         filepath,         process,