fix appveyor installing wrong v of dotnet.

appveyor.yml

@@ -1,17 +1,12 @@
 version: 0.2.0.{build}
 os: Visual Studio 2017
 install:
-  - if not exist dotnet-dev-win-x64.latest.zip appveyor DownloadFile https://dotnetcli.blob.core.windows.net/dotnet/Sdk/master/dotnet-dev-win-x64.latest.zip -FileName "dotnet-dev-win-x64.latest.zip"  
-  - cmd: 7z x dotnet-dev-win-x64.latest.zip -oc:\dotnet
 
 before_build:
 - cmd: git submodule update --init --recursive
-- cmd: path c:\dotnet
-- cmd: dotnet --info  
 
 build_script:
 - cmd: dotnet --info
-- ps: path c:\dotnet
 - ps: .\build.ps1
 
 test: off