[cmake] upgrade cmake version to eliminate deprecation warning

[lavnFan]

when I use websocktpp in my project, then comes camke version warning:

C/C++: debug|arm64-v8a :CMake Deprecation Warning at D:/Hippy/driver/js/android/.cxx/Debug/2e504n4g/arm64-v8a/_deps/websocketpp-src/CMakeLists.txt:5 (cmake_minimum_required): C/C++: debug|arm64-v8a : Compatibility with CMake < 2.8.12 will be removed from a future version of C/C++: debug|arm64-v8a : CMake. C/C++: debug|arm64-v8a : Update the VERSION argument value or use a ... suffix to tell C/C++: debug|arm64-v8a : CMake that the project does not need compatibility with older versions.

so should we upgrade cmake version to 2.8.12