Name specified in ghc-mod.vim is ghc_mod, not ghc-mod.

After updating syntastic to head, I was unable to get error reporting for haskell files, altough hlint was working properly. Turns out that in *syntax_checkers/haskell/ghc-mod.vim* the name is specified as ```ghc_mod```, while in the registry it was ```ghc-mod```.

This should fix it.
Cheers!