Update last position

[mauroat22]

Update last position self.lastPosition = position after scrolling programatically to prevent discordances between scrolling and selecting by clicking, for instance.

    public func moveTo(position: CGFloat) {
        self.lastPosition = position
        self.position = self.correctPositionInRange(position: position)
    }

[AndrewSB]

is this still an issue? I'm about to use this library but this worries me, I'm not programmatically setting scroll offsets yet, but I probably will soon