Update plotly to 2.7.0

[pyup-bot]

This PR updates plotly from 2.5.1 to 2.7.0.

Changelog

2.7.0

Updated
- Updated `plotly.min.js` to version 1.38.0.
- New features include a `3D cone` trace to visualize vector fields.
- See [the plotly.js CHANGELOG](https://github.com/plotly/plotly.js/blob/master/CHANGELOG.md1380----2018-05-23) for additional information regarding the updates.

2.6.0

Updated
- Updated `plotly.min.js` to version 1.37.1.
- New features include a `splom` (scatter plot matrix) trace type.
- See [the plotly.js CHANGELOG](https://github.com/plotly/plotly.js/blob/master/CHANGELOG.md1371----2018-05-02) for additional information regarding the updates.
- Error message for `plotly.figure_factory.create_choropleth` is more helpful for Windows users on installing `geopandas` and dependencies including `shapely`.

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 147

• 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 59.446%

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Totals
Change from base Build 110:	0.0%
Covered Lines:	4204
Relevant Lines:	7072

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💛 - Coveralls