Update plotly to 3.1.0

[pyup-bot]

This PR updates plotly from 3.0.2 to 3.1.0.

Changelog

Links

• PyPI: https://pypi.org/project/plotly
• Changelog: https://pyup.io/changelogs/plotly/
• Homepage: https://plot.ly/python/

[coveralls]

Pull Request Test Coverage Report for Build 287

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 61.074%

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Totals
Change from base Build 284:	0.0%
Covered Lines:	4616
Relevant Lines:	7558

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💛 - Coveralls

[pyup-bot]

Closing this in favor of #78