s/2.15/2.14.4/

See https://github.com/haskell/cabal/issues/1721#issuecomment-52210898

Cabal/Distribution/Simple/Haddock.hs

@@ -408,7 +408,7 @@ renderArgs verbosity tmpFileOpts version comp args k = do
   createDirectoryIfMissingVerbose verbosity True outputDir
   withTempFileEx tmpFileOpts outputDir "haddock-prolog.txt" $ \prologFileName h -> do
           do
-             when (version >= Version [2,15] []) (hSetEncoding h utf8)
+             when (version >= Version [2,14,4] []) (hSetEncoding h utf8)
              hPutStrLn h $ fromFlag $ argPrologue args
              hClose h
              let pflag = "--prologue=" ++ prologFileName