PYTHON_INCLUDE_DIR => PYTHON_INCLUDE_PATH for compatibility with older cmake version

gmshpy/CMakeLists.txt

@@ -70,7 +70,7 @@ if(ENABLE_PYTHON_LIB_API)
 endif(ENABLE_PYTHON_LIB_API)
 
 include(${SWIG_USE_FILE})
-include_directories(${PYTHON_INCLUDE_DIR})
+include_directories(${PYTHON_INCLUDE_PATH})
 
 foreach(module ${SWIG_MODULES})
   set_source_files_properties(${module}.i PROPERTIES CPLUSPLUS ON)