Update conf.py

Attempt to fix plotly again as proposed in readthedocs/sphinx_rtd_theme#788 (comment)

docs/conf.py

@@ -44,6 +44,13 @@
     "jupyter_sphinx",
 ]
 
+nbsphinx_prolog = r"""
+.. raw:: html
+
+    <script src='http://cdnjs.cloudflare.com/ajax/libs/require.js/2.1.10/require.min.js'></script>
+    <script>require=requirejs;</script>
+"""
+
 # Autosummary pages will be generated by sphinx-autogen instead of sphinx-build
 autosummary_generate = []