Update AppVeyor to use Start-PSBootstrap

appveyor.yml

@@ -18,13 +18,10 @@ install:
   - ps: Set-Content c:\users\appveyor\.ssh\id_rsa $fileContent
   - git config --global url.git@github.com:.insteadOf https://github.com/
   - git submodule update --init -- src/windows-build src/Modules/Pester
-  - ps: Invoke-WebRequest -Uri https://raw.githubusercontent.com/dotnet/cli/rel/1.0.0/scripts/obtain/install.ps1 -OutFile install.ps1
-  - ps: ./install.ps1 -version 1.0.0-beta-002198
+  - ps: Import-Module .\PowerShellGitHubDev.psm1; Start-PSBootstrap
 
 build_script:
   - ps: |
-      $env:Path += ";$env:LocalAppData\Microsoft\dotnet\cli"
-      dotnet --version
       Import-Module .\PowerShellGitHubDev.psm1
       Start-PSBuild -Publish
       Start-PSBuild -FullCLR