Travis: solve dep constraints before build
Travis: solve dep constraints before build

ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ssaavedra/liquidhaskell,ssaavedra/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell,ucsd-progsys/liquidhaskell,ucsd-progsys/liquidhaskell,ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell,ucsd-progsys/liquidhaskell,ssaavedra/liquidhaskell