message: try to put "image" in the build matrix
diff: # http://www.appveyor.com/docs/appveyor-yml
  -image: Visual Studio 2017
  -
  notifications:
  - provider: Email
  on_build_status_changed: false
  @@ -26,6 +24,7 @@ matrix:
  environment:
  matrix:
  - platform: x86
  + image: Visual Studio 2017
  configuration: Debug
  arch: "Win32"
  VS_GEN: ""
  