pin appveyor image

appveyor.yml

@@ -1,6 +1,9 @@
 version: "master-{build}"
 
-os: Windows Server 2012 R2
+# fix for retrieving progress information for local execution
+# see: http://help.appveyor.com/discussions/problems/5170-progresspreference-not-works-always-shown-preparing-modules-for-first-use-in-stderr
+image: Previous Visual Studio 2015
+
 platform:
   - x64
 
@@ -45,6 +48,7 @@ install:
   - gem install --local bundler --quiet --no-document
   - bundler --version
   - ruby -r rubygems -e "p Gem.path"
+  - ps: Write-Output "Echo"
 
 build_script:
   - bundle install --path=vendor/bundle --without integration tools