Add requests[security] for python 2.6.

Author: theengineear

setup.py

@@ -42,5 +42,6 @@ def readme():
                 'plotly/matplotlylib/mplexporter/renderers'],
       package_data={'plotly': ['graph_reference/*.json', 'widgets/*.js']},
       install_requires=['requests', 'six', 'pytz'],
-      extras_require={"PY2.6": ['simplejson', 'ordereddict']},
+      extras_require={"PY2.6": ['simplejson', 'ordereddict',
+                                'requests[security]']},
       zip_safe=False)