Updated .NET Core CI version

Author: Turnerj

.appveyor.yml

@@ -7,7 +7,7 @@ services:
 install:
   - choco install opencover.portable codecov
   - choco install Memurai-Developer --version 2.0.0
-  - ps: .\build\dotnet-install.ps1 -Version 3.0.100
+  - ps: .\build\dotnet-install.ps1 -Version 3.1.202
 
 build_script:
   - ps: .\build.appveyor.ps1