conduit-extra to build-depends in xournal-parser.cabal

Hello,

I added added 'conduit-extra' to build-depends in cabal file to resolve the following hidden package message when building package:

    src/Text/Xournal/Parse/Conduit.hs:28:18:
    Could not find module `Data.Conduit.Zlib'
    It is a member of the hidden package `conduit-extra-1.1.0'.
    Perhaps you need to add `conduit-extra' to the build-depends in your .cabal file.