Trying suggestion from wieslawsoltes

appveyor.yml

@@ -11,10 +11,10 @@ environment:
     secure: OtVfyN3ErqQrDTnWH2HDfJDlCiu/i4/X4wFmK3ZXXP7HmCiXYPSbTjMPwwdOxRaK
   MYGET_API_URL: https://www.myget.org/F/avalonia-ci/api/v2/package
 install:
-  - if not exist dotnet-1.0.1.exe appveyor DownloadFile https://go.microsoft.com/fwlink/?linkid=843448 -FileName "dotnet-1.0.1.exe"
   - if not exist gtk-sharp-2.12.26.msi appveyor DownloadFile http://download.xamarin.com/GTKforWindows/Windows/gtk-sharp-2.12.26.msi
-  - msiexec /i gtk-sharp-2.12.26.msi /qn /norestart
-  - cmd: call dotnet-1.0.1.exe /quiet
+  - if not exist dotnet-1.0.1.exe appveyor DownloadFile https://go.microsoft.com/fwlink/?linkid=843448 -FileName "dotnet-1.0.1.exe"
+  - ps: Start-Process -FilePath "msiexec" -ArgumentList "/i gtk-sharp-2.12.26.msi /quiet /qn /norestart" -Wait
+  - ps: Start-Process -FilePath "dotnet-1.0.1.exe" -ArgumentList "/quiet" -Wait
   - cmd: set PATH=%programfiles(x86)%\GtkSharp\2.12\bin\;%PATH%
 before_build:
 - git submodule update --init