Conduit test suite build failure with ghc 8.4

[DanBurton]

[3 of 5] Compiling StreamSpec       ( test/StreamSpec.hs, dist/build/conduit-test/conduit-test-tmp/StreamSpec.o )

test/StreamSpec.hs:466:10: error:
    • Could not deduce (Prelude.Semigroup (Sum a))
        arising from the superclasses of an instance declaration
      from the context: Prelude.Num a
        bound by the instance declaration at test/StreamSpec.hs:466:10-40
      There are instances for similar types:
        instance Prelude.Num a =>
                 Prelude.Semigroup (base-4.11.0.0:Data.Semigroup.Internal.Sum a)
          -- Defined in ‘base-4.11.0.0:Data.Semigroup.Internal’
    • In the instance declaration for ‘Monoid (Sum a)’
    |
466 | instance Prelude.Num a => Monoid (Sum a) where
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^