fix typo

Author: isuruf

appveyor.yml

@@ -107,7 +107,7 @@ install:
 - mkdir build
 - cd build
 
-- if [%COMPILER%]==[MSVC15] set "CMAKE_GENERATOR=Visual Studio 14 2019"
+- if [%COMPILER%]==[MSVC15] set "CMAKE_GENERATOR=Visual Studio 16 2019"
 - if [%COMPILER%]==[MSVC15] set "CMAKE_GENERATOR_PLATFORM=%PLATFORM%"
 - if [%COMPILER%]==[MinGW]  set "CMAKE_GENERATOR=MinGW Makefiles"
 - if [%COMPILER%]==[MinGW-w64] set "CMAKE_GENERATOR=MinGW Makefiles"