Fix haddock-test to work with latest version of Cabal.
Fix haddock-test to work with latest version of Cabal.

Signed-off-by: Edward Z. Yang <dbd597f5635f432486c5d365e9bb585b3eaa1853@cs.stanford.edu>

haskell/haddock,haskell/haddock,haskell/haddock,haskell/haddock,haskell/haddock