lower-case PEP263 encoding declaration

so emacs likes it...

port/PyAssimp/pyassimp/structs.py

@@ -1,4 +1,4 @@
-#-*- coding: UTF-8 -*-
+#-*- coding: utf-8 -*-
 
 from ctypes import POINTER, c_void_p, c_uint, c_char, c_float, Structure, c_char_p, c_double, c_ubyte, c_size_t, c_uint32