Require a minimum version of decorator, fixes #721

Author: chriddyp

Diff for: setup.py

@@ -46,7 +46,7 @@ def readme():
                 'plotly/matplotlylib/mplexporter',
                 'plotly/matplotlylib/mplexporter/renderers'],
       package_data={'plotly': ['package_data/*']},
-      install_requires=['decorator',
+      install_requires=['decorator>=4.0.6',
                         'nbformat>=4.2',
                         'pytz',
                         'requests',