Switches AppVeyor to use VS 2017 (#76)

* Switches AppVeyor to use VS 2017

Should massively speed up builds

* Update appveyor.yml

Author: ThadHouse

appveyor.yml

@@ -8,21 +8,6 @@ branches:
 nuget:
   disable_publish_on_pr: true
 
-install:
-##   # .NET Core SDK binaries
-##   ## 1) from direct url  
-##   - ps: $url = "https://go.microsoft.com/fwlink/?LinkID=798402" # v1.0.0-preview1 x64
-##   ## 2) from url based on version, for example using an env var CLI_VERSION that can be a
-##   ##    a specific version `1.0.0-preview2-003121` or `Latest` (for latest dev version)
-- ps: $url = "https://dotnetcli.blob.core.windows.net/dotnet/Sdk/rel-1.0.0/dotnet-dev-win-x64.latest.zip"
-# Download .NET Core SDK and add to PATH
-- ps: $env:DOTNET_INSTALL_DIR = "$pwd\.dotnetsdk"
-- ps: mkdir $env:DOTNET_INSTALL_DIR -Force | Out-Null
-- ps: $tempFile = [System.IO.Path]::GetTempFileName()
-- ps: (New-Object System.Net.WebClient).DownloadFile($url, $tempFile)
-- ps: Add-Type -AssemblyName System.IO.Compression.FileSystem; [System.IO.Compression.ZipFile]::ExtractToDirectory($tempFile, $env:DOTNET_INSTALL_DIR)
-- ps: $env:Path = "$env:DOTNET_INSTALL_DIR;$env:Path"
-
 build_script:
 - ps: .\build.ps1