Update plotly to 3.7.1

[pyup-bot]

This PR updates plotly from 3.6.1 to 3.7.1.

Changelog

3.7.1

Fixed
- Fixed `.update` on numbered axis objects for Python < 3.6
([1462](https://github.com/plotly/plotly.py/issues/1462),
[1464](https://github.com/plotly/plotly.py/pull/1464))

3.7.0

Updated
- Updated Plotly.js to version 1.45.2. See the
[plotly.js CHANGELOG](https://github.com/plotly/plotly.js/blob/master/CHANGELOG.md1452----2019-03-07)
for more information.

Added
- Added new `auto_play` argument to offline `plot` and `iplot` to control
whether figures with frames are automatically animated when the figure is
loaded
([1447](https://github.com/plotly/plotly.py/pull/1447))
- Added support for uploading "offline" animations (those with inline data
arrays rather than grid references) to Chart Studio using `plotly.plotly.create_animations`
([1432](https://github.com/plotly/plotly.py/pull/1432))

Updated
- Updated implementation of the `ternary_contour` figure factory that was
added in 3.6.0. The new implementation uses the native plotly.js ternary axes
and provides ILR transform support.
([1418](https://github.com/plotly/plotly.py/pull/1418))

Fixed
- Make sure the trace `selectedpoints` property of `FigureWidget` traces is
updated on the Python side in response to plotly.js selection events
([1433](https://github.com/plotly/plotly.py/issues/1433))
- Fix validation for 0-dimensional numpy arrays
([1444](https://github.com/plotly/plotly.py/pull/1444)). Special thanks to 
[ankokumoyashi](https://github.com/ankokumoyashi) for this contribution!

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 690

• 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 54.988%

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Totals
Change from base Build 687:	0.0%
Covered Lines:	4823
Relevant Lines:	8771

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💛 - Coveralls