File "/app/.heroku/python/lib/python2.7/site-packages/pyiso/miso.py", line 43, in get_generation
data = self.latest_fuel_mix()
File "/app/.heroku/python/lib/python2.7/site-packages/pyiso/miso.py", line 116, in latest_fuel_mix
df.index = self.utcify_index(df.index)
File "/app/.heroku/python/lib/python2.7/site-packages/pyiso/base.py", line 418, in utcify_index
aware_local_index = local_index.tz_localize(tz_name)
AttributeError: 'Index' object has no attribute 'tz_localize'