Switch to python3

--- a/lib/github/commands/rest2html
+++ b/lib/github/commands/rest2html
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """
 rest2html - A small wrapper file for parsing ReST files at GitHub.
 
@@ -30,12 +30,6 @@
 import sys
 import os
 
-# This fixes docutils failing with unicode parameters to CSV-Table. The -S
-# switch and the following 3 lines can be removed after upgrading to python 3.
-if sys.version_info[0] < 3:
-    reload(sys)
-    sys.setdefaultencoding('utf-8')
-
 import site
 
 try:
--- a/lib/github/markups.rb
+++ b/lib/github/markups.rb
@@ -45,7 +45,7 @@
 
 command(
   ::GitHub::Markups::MARKUP_RST,
-  "python2 -S #{Shellwords.escape(File.dirname(__FILE__))}/commands/rest2html",
+  "python3 #{Shellwords.escape(File.dirname(__FILE__))}/commands/rest2html",
   /re?st(\.txt)?/,
   ["reStructuredText"],
   "restructuredtext"