trifecta bump needed

[ilovezfs]

With GHC 8.0.2 and Cabal 2.0.0.0 the build fails in a Cabal sandbox with the error

Building trifecta-1.6.2.1...
Preprocessing library trifecta-1.6.2.1...
[ 1 of 13] Compiling Text.Trifecta.Util.IntervalMap ( src/Text/Trifecta/Util/IntervalMap.hs, dist/dist-sandbox-f96742a3/build/Text/Trifecta/Util/IntervalMap.o )
[ 2 of 13] Compiling Text.Trifecta.Util.Combinators ( src/Text/Trifecta/Util/Combinators.hs, dist/dist-sandbox-f96742a3/build/Text/Trifecta/Util/Combinators.o )
[ 3 of 13] Compiling Text.Trifecta.Util.Array ( src/Text/Trifecta/Util/Array.hs, dist/dist-sandbox-f96742a3/build/Text/Trifecta/Util/Array.o )
[ 4 of 13] Compiling Text.Trifecta.Instances ( src/Text/Trifecta/Instances.hs, dist/dist-sandbox-f96742a3/build/Text/Trifecta/Instances.o )

src/Text/Trifecta/Instances.hs:18:10: error:
    Duplicate instance declarations:
      instance Data.Semigroup Doc
        -- Defined at src/Text/Trifecta/Instances.hs:18:10
      instance [safe] Data.Semigroup Doc
        -- Defined in ‘Text.PrettyPrint.ANSI.Leijen.Internal’
Failed to install trifecta-1.6.2.1
cabal: Error: some packages failed to install:
dhall-1.5.1-AIPTNjvj7BN5FxlhYpbUg7 depends on dhall-1.5.1 which failed to
install.
trifecta-1.6.2.1-2vPOScXwOhmFuR3MyAzULj failed during the building phase. The
exception was:
ExitFailure 1

Full build log https://gist.github.com/ilovezfs/4f84b5165dd7538d34eb147bf805e668

[ilovezfs]

Thanks!