Update appveyor.yml

Author: pdimov

appveyor.yml

@@ -28,9 +28,13 @@ environment:
       TOOLSET: clang-win
       CXXSTD: 14,17,latest
       ADDRMD: 64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      TOOLSET: msvc-14.2
+      CXXSTD: 14,17,20,latest
+      ADDRMD: 32,64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       TOOLSET: clang-win
-      CXXSTD: 14,17,latest
+      CXXSTD: 14,17,20,latest
       ADDRMD: 64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
       ADDPATH: C:\cygwin\bin;