[#106] reduce ci job to 4 cores

.gitlab-ci.yml

@@ -66,7 +66,7 @@ build_win10_mingw:
     - mkdir debug
     - cd debug
     - cmake --no-warn-unused-cli -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -DCMAKE_BUILD_TYPE:STRING=Debug -DCMAKE_C_COMPILER:FILEPATH=C:\msys64\mingw64\bin\x86_64-w64-mingw32-gcc.exe -DCMAKE_CXX_COMPILER:FILEPATH=C:\msys64\mingw64\bin\x86_64-w64-mingw32-g++.exe .. -G "Unix Makefiles"
-    - cmake --build . -j 8
+    - cmake --build . -j 4
 
 build_mac_clang:
   only: