mapbox marker symbol not working

[bcdunbar]

marker symbols in scattermapbox either don't show up or don't color correctly. For example, 'star' is visible but is always black; square isn't visible.

https://codepen.io/bcd/pen/EpVaxQ?editors=1010

I see there a few issue concerning symbols specific to IE or Edge. This isn't browser-specific.

[etpinard]

Scattermapbox doesn't share the same marker symbol list as our other scatter* trace type

plotly.js/src/traces/scattermapbox/attributes.js

Lines 72 to 84 in 918ed9c

	marker: {
	symbol: {
	valType: 'string',
	dflt: 'circle',
	role: 'style',
	arrayOk: true,
	description: [
	'Sets the marker symbol.',
	'Full list: https://www.mapbox.com/maki-icons/',
	'Note that the array `marker.color` and `marker.size`',
	'are only available for *circle* symbols.'
	].join(' ')
	},

The list in https://www.mapbox.com/maki-icons/ seems to change fairly frequently, and yes some markers can't be shown in color, but there's not much we can do about it.

[etpinard]

merging with #815