fix(mge/build): update cmake_minimum_required VERSION

Fixed according to the case mentioned in Issue #57 opened by @zjd1988 .   

```
Policy "CMP0086" is not known to this version of CMake. Starting with CMake 3.14, UseSWIG passes option -module <module_name> to SWIG compiler if the file property SWIG_MODULE_NAME is specified. This policy provides compatibility with projects that expect the legacy behavior.
```

CMakeLists.txt

-cmake_minimum_required(VERSION 3.13.0)
+cmake_minimum_required(VERSION 3.14.4)
 
 include (cmake/FetchMegBrainVersion.cmake)
 project(MegEngine LANGUAGES C CXX VERSION ${MGB_VER_STRING})