Always use scale.x for getBarWidth

[bijection]

Victory-bar handles switching the x and y scales for horizontal bars in getCalculatedValues:

const scale = {
  x: horizontal ? yScale : xScale,
  y: horizontal ? xScale : yScale
};

Currently, the getBarWidth function switches them again to calculate width:

const range = horizontal ? scale.y.range() : scale.x.range();

Because of this, horizontal Bars rendered by VictoryBar actually end up using their VictoryBar's xScale to determine their widths. This results in the following bug:

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--- | ---

This patch remediates the problem by always using scale.x in getBarWidth, under the assumption that scale.x will in fact be a parent VictoryBar's yScale if the Bar is horizontal.

[boygirl]

@bijection thanks for this change!