Remove -S flag for python3

This should not be necessary anymore and its presence breaks actual use
of pip which installs into the site-packages directory.

Author: Carl Brasic

lib/github/markups.rb

@@ -49,7 +49,7 @@
 
 command(
   ::GitHub::Markups::MARKUP_RST,
-  "python3 -S #{Shellwords.escape(File.dirname(__FILE__))}/commands/rest2html",
+  "python3 #{Shellwords.escape(File.dirname(__FILE__))}/commands/rest2html",
   /re?st(\.txt)?/,
   ["reStructuredText"],
   "restructuredtext"