Update appveyor.yml

Try this solution https://gitlab.kitware.com/cmake/cmake/commit/27eb7c5bdb5bb8deefe1772675dc4819592bf036

appveyor.yml

@@ -31,7 +31,7 @@ install:
   - if "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2015" set CMAKE_GENERATOR_NAME=Visual Studio 14 2015
   - if "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2017" set CMAKE_GENERATOR_NAME=Visual Studio 15 2017
   - if "%platform%"=="x64" set CMAKE_GENERATOR_NAME=%CMAKE_GENERATOR_NAME% Win64
-  - cmake %CMAKE_DEFINES% -G "%CMAKE_GENERATOR_NAME%"
+  - cmake %CMAKE_DEFINES% -G "%CMAKE_GENERATOR_NAME%" .
   - set PATH=%PATH%;"C:\\Program Files (x86)\\Inno Setup 5"
   - ps: Invoke-WebRequest -Uri https://download.microsoft.com/download/5/7/b/57b2947c-7221-4f33-b35e-2fc78cb10df4/vc_redist.x64.exe -OutFile .\packaging\windows-innosetup\vc_redist.x64.exe
   - ps: Invoke-WebRequest -Uri https://download.microsoft.com/download/1/d/8/1d8137db-b5bb-4925-8c5d-927424a2e4de/vc_redist.x86.exe -OutFile .\packaging\windows-innosetup\vc_redist.x86.exe