Python 3.6 syntax fixes

doc/build/conf.py

diff --git a/doc/build/conf.py b/doc/build/conf.py
index 807782b..605af5a 100644
--- a/doc/build/conf.py
+++ b/doc/build/conf.py
@@ -208,8 +208,8 @@
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title, author, documentclass [howto/manual]).
 latex_documents = [
-  ('index', 'mako_%s.tex' % release.replace('.', '_'), ur'Mako Documentation',
-   ur'Mike Bayer', 'manual'),
+  ('index', 'mako_%s.tex' % release.replace('.', '_'), u'Mako Documentation',
+   u'Mike Bayer', 'manual'),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of