consider pybind11 include directory before python

This is needed in case an older pybind11 version was installed with pip
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2996e53..4440b90 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,12 +84,12 @@
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra")
 endif()
 
-# Include path for Python header files
-include_directories(${PYTHON_INCLUDE_DIR})
-
 # Include path for pybind11 header files
 include_directories(include)
 
+# Include path for Python header files
+include_directories(${PYTHON_INCLUDE_DIR})
+
 set(PYBIND11_HEADERS
   include/pybind11/attr.h
   include/pybind11/cast.h