use VS2017 image

appveyor.yml

@@ -1,26 +1,13 @@
-
 version: 0.0.{build}
-
-environment:
-  # Set the DOTNET_SKIP_FIRST_TIME_EXPERIENCE environment variable to stop wasting time caching packages
-  DOTNET_SKIP_FIRST_TIME_EXPERIENCE: true
-  # Disable sending usage data to Microsoft
-  DOTNET_CLI_TELEMETRY_OPTOUT: true
+image: Visual Studio 2017
 
 install:
-  # Use the install script to grab the latest dotnet install
-  - ps: iex .\dotnet-latest.ps1
   - choco install gitversion.portable -pre -y
-  # Prepend newly installed dotnet cli to the PATH of this build (this cannot be
-  # done from inside the powershell script as it would require to restart
-  # the parent CMD process).
-  - "SET PATH=C:\\Users\\appveyor\\AppData\\Local\\Microsoft\\dotnet\\;%PATH%"  
 
 before_build:
   - cmd: dotnet --version
   - ps: gitversion /l console /output buildserver
 
-
 build_script:
   - cmd: build.cmd
   - cmd: tests\CodeCoverage\CodeCoverage.cmd