Same startColor and endColor produces unnecessary gradient

[xquezme]

I assume, this because library uses !== instead of !=, but .cgColor always produce different instance. And pointers are not equal.

Example:

let view = RingProgressView()
view.startColor = .red
view.endColor = .red

Workaround:

let view = RingProgressView()
let color = UIColor.red.cgColor
let layer = (view.layer as! RingProgressLayer)
layer.startColor = color
layer.endColor = color

[maxkonovalov]

Yes, indeed, in some cases the check would produce incorrect result, I pushed a fix.