Make snippets executable

snippets/test_diff.py

@@ -1,3 +1,5 @@
+#!/usr/bin/env python3
+
 from birdvisu import maps
 from pprint import pprint
 import sys

snippets/test_ospffile.py

@@ -1,4 +1,4 @@
-#!/bin/python3
+#!/usr/bin/env python3
 
 from birdvisu import ospffile
 from pprint import pprint