ci: Use the previous build worker image in AppVeyor

hebasto · hebasto · commit 406097c8102d · 2020-11-15T09:12:06.000+02:00
This is a workaround as the recent Visual Studio 2019 image update
breaks our builds.
diff --git a/.appveyor.yml b/.appveyor.yml
@@ -1,6 +1,6 @@
 version: '{branch}.{build}'
 skip_tags: true
-image: Visual Studio 2019
+image: Previous Visual Studio 2019
 configuration: Release
 platform: x64
 clone_depth: 5
