message: appveyor: use visual studio 2019 in build
diff: @@ -20,7 +20,7 @@ install:
  - "cd antlr4/runtime/Cpp"
  - "mkdir build"
  - "cd build"
  - - 'cmake -G "Visual Studio 15 2017 Win64" -DWITH_STATIC_CRT=Off -DCMAKE_BUILD_TYPE=Release ..'
  + - 'cmake -G "Visual Studio 15 2019 Win64" -DWITH_STATIC_CRT=Off -DCMAKE_BUILD_TYPE=Release ..'
  - "msbuild LIBANTLR4.sln /p:configuration=Release" # for other configuration installation does not work currently
  - "cmake -P cmake_install.cmake"
  - "cd ../../../../"
  