Fix typo in package provider name

Author: StefanScherer

appveyor.yml

@@ -2,8 +2,8 @@ version: 1.0.{build}
 image: Visual Studio 2017
 
 build_script:
+  - ps: Install-Package -Name docker -ProviderName DockerMsftProvider -RequiredVersion 17.06.0-ce
+  - ps: start-service docker
   - docker pull microsoft/windowsservercore
   - docker pull microsoft/nanoserver
-  - ps: Install-Package -Name docker -ProviderName DockerMsftProviderInsider -RequiredVersion 17.06.0-ce
-  - ps: start-service docker
   - ps: .\test-build.ps1