include nbformat as dependency to fix plotly#692

Author: chriddyp

setup.py

@@ -45,5 +45,9 @@ def readme():
                 'plotly/matplotlylib/mplexporter',
                 'plotly/matplotlylib/mplexporter/renderers'],
       package_data={'plotly': ['package_data/*']},
-      install_requires=['decorator', 'requests', 'six', 'pytz'],
+      install_requires=['decorator',
+                        'nbformat>=4.3',
+                        'pytz',
+                        'requests',
+                        'six'],
       zip_safe=False)