Update Python docgen
diff --git a/setup.py b/setup.py
index cfb578e..cf5ab49 100644
--- a/setup.py
+++ b/setup.py
@@ -154,6 +154,7 @@
 
 SETUP_REQUIRES = (
     'sphinx>=1.3',
+    'sphinx_rtd_theme>=0.1.8'
 ) + INSTALL_REQUIRES
 
 COMMAND_CLASS = {