try to fix problem...

appveyor.yml

 configuration: Release
-image: Visual Studio 2019
+image: Visual Studio 2017
 platform: x64
 
 cache: c:\tools\vcpkg\installed\
 
 install:
     - cd C:\projects\libswf && git submodule update --init --recursive
-    - call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars64.bat"
+    - call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
     - cd C:\Tools\vcpkg && git pull && .\bootstrap-vcpkg.bat && cd %APPVEYOR_BUILD_FOLDER%
     - vcpkg install zlib:x64-windows zlib:x64-windows-static
     - vcpkg integrate install
 
 before_build:
     - mkdir build && cd build
-    # https://stackoverflow.com/questions/44478492/cmake-failed-to-run-msbuild-command-msbuild-exe
-    # https://help.appveyor.com/discussions/questions/2847-cmake-update-with-chocolatey
-    - set PATH=C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin;%PATH%
     - cmake ..
        -DCMAKE_BUILD_TYPE:STRING=Release
        -DCMAKE_TOOLCHAIN_FILE=C:/Tools/vcpkg/scripts/buildsystems/vcpkg.cmake
-       -G "Visual Studio 16 2019" -A Win64
+       -G "Visual Studio 14 2017 Win64"
 
 build:
     project: $(APPVEYOR_BUILD_FOLDER)\build\$(APPVEYOR_PROJECT_NAME).sln
\ No newline at end of file