Merge pull request #128 from dougfelt/fix_find_python

Fix scripts that auto-invoke python to find it correctly.

generate_emoji_html.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc. All rights reserved.
 #

materialize_emoji_images.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 #
 # Copyright 2016 Google Inc. All rights reserved.
 #