Update online demo URL

My Heroku account was recently running out of free dyno hours pretty quickly
diff --git a/README.rst b/README.rst
index 2870658..250ef3f 100644
--- a/README.rst
+++ b/README.rst
@@ -36,7 +36,7 @@
 programmer would write if they were following the style guide. It takes away
 some of the drudgery of maintaining your code.
 
-Try out YAPF with this `online demo <https://yapf.herokuapp.com>`_.
+Try out YAPF with this `online demo <https://yapf.now.sh>`_.
 
 .. footer::