Allow PolylinePipeline.generateArc to accept an array of heights for one position

[hpinkos]

PolylinePipeline.generateArc accepts either a number or array of numbers for the height value. However, if there was only one position, the function was only expecting height to be a number instead of an array. This adds a check so I can do something like this:

var newPositions = PolylinePipeline.generateArc({
    positions: [myPosition],
    height: [30]
});

[pjcozzi]

Good catch. Update CHANGES.md with this minor fix.

[hpinkos]

@pjcozzi ready

[pjcozzi]

Thanks!