Scatter3d `right` textalignment overlaps points

[jonmmease]

One of two issues reported in plotly/plotly.py#1055

CodePen: https://codepen.io/anon/pen/qyKLLe

For a scatter3d trace, setting the textposition property to "middle left" causes the text to be displayed nicely to the left of the points:

Setting the property to "middle right" causes the text to overlap the associated point:

It looks like the text alignment is correctly changed, but an offset is needed to push the text anchor to the right. The 2D scatter trace does not have this issue.