Fix building docs with nbsphinx

Author: takluyver

docs/source/conf.py

@@ -43,10 +43,7 @@
 templates_path = ['_templates']
 
 # The suffix(es) of source filenames.
-# You can specify multiple suffix as a list of string:
-#
-# source_suffix = ['.rst', '.md']
-source_suffix = ['.rst', '.ipynb']
+source_suffix = {'.rst': 'restructuredtext'}
 
 # The master toctree document.
 master_doc = 'index'