Use Visual Studio Community 2019 version 16.3.4 image

Tasteful · Tasteful · commit 5a3c9e95b4db · 2019-10-22T14:26:56.000+02:00
diff --git a/appveyor.yml b/appveyor.yml
@@ -5,7 +5,7 @@ branches:
   only:
     - master
     - development
-image: Visual Studio 2017
+image: Visual Studio 2019
 nuget:
   disable_publish_on_pr: true
 environment:
