Update appveyor, install dnvm
Update appveyor, install dnvm

RichiCoder1/omnisharp-atom,rambocoder/omnisharp-atom,rambocoder/omnisharp-atom,RichiCoder1/omnisharp-atom,OmniSharp/omnisharp-atom,OmniSharp/omnisharp-atom,OmniSharp/omnisharp-atom,rambocoder/omnisharp-atom,RichiCoder1/omnisharp-atom,RichiCoder1/omnisharp-atom