deploying plotly in heroku generates this error

[kundami]

packages/matplotlib/backends/backend_tkagg.py", line 6, in
2018-02-27T04:11:03.474771+00:00 app[web.1]: return _import_module(self.mod)
2018-02-27T04:11:03.474806+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/six.py", line 82, in _import_module
2018-02-27T04:11:03.475004+00:00 app[web.1]: import(name)
2018-02-27T04:11:03.475039+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/tkinter/init.py", line 36, in
2018-02-27T04:11:03.475223+00:00 app[web.1]: import _tkinter # If this fails your Python may not be configured for Tk
2018-02-27T04:11:03.475268+00:00 app[web.1]: ModuleNotFoundError: No module named '_tkinter'
2018-02-27T04:11:03.931029+00:00 heroku[web.1]: State changed from starting to crashed
2018-02-27T04:11:
03.914181+00:00 heroku[web.1]: Process exited with status 1