Update for newest Happy (GHC 7.8 compat)

I don't particularly know if this has any effect, but the newest version of Happy seems to give this line the boot. Refer to http://ro-che.info/articles/2014-03-08-happy-alex-ghc-7.8.html for more info. I'm pretty sure this is extremely low priority, but the build goes fine and I haven't seen any issues in my IHaskell build.