AppVeyor fails installing GHC 7.10.3
AppVeyor fails installing GHC 7.10.3

This fixes #3687

Swithed AppVeyor test to GHC 8.0.1 because 7.10.3 is broken (https://chocolatey.org/packages/ghc/7.10.3) and added the `-y` option and `refreshenv` after installing GHC as suggested by Chocolatey
themoritz/cabal,sopvop/cabal,themoritz/cabal,sopvop/cabal,themoritz/cabal,sopvop/cabal,mydaum/cabal,mydaum/cabal