iOS swift3 Chart xaxis duplicate value issue

I have an issue creating a string value for xAxis using the iOS Charts library

x value always has duplicate value, see following picture, you can see value always be JAN JAN JAN JAN FEB FEB FEB

How I can setup chart's x value as it will show JAN FEB MAR ?

import UIKit
import Charts
class ViewController: UIViewController {
var months:[String]!
@IBOutlet var lineChartView: LineChartView!

override func viewDidLoad() {
super.viewDidLoad()


let unitsSold = [20.0, 4.0, 6.0]

var months = ["Jan", "Feb", "Mar"]

let formato:LineChartFormatter = LineChartFormatter(labels: months)
let xaxis:XAxis = XAxis()

var dataEntries: [ChartDataEntry] = []

for i in 0..<unitsSold.count {
let dataEntry = ChartDataEntry(x: Double(i), y: unitsSold[i])

print("double \(Double(i))")
dataEntries.append(dataEntry)
}

xaxis.valueFormatter = formato
let data = LineChartData()
let dataset = LineChartDataSet(values: dataEntries, label: "Hello")
dataset.colors = [NSUIColor.red]
data.addDataSet(dataset)


self.lineChartView.gridBackgroundColor = NSUIColor.white
self.lineChartView.xAxis.drawGridLinesEnabled = true;
self.lineChartView.xAxis.labelPosition = XAxis.LabelPosition.bottom
self.lineChartView.xAxis.centerAxisLabelsEnabled = true
self.lineChartView.chartDescription?.text = "LineChartView Example"
self.lineChartView.xAxis.valueFormatter = xaxis.valueFormatter
self.lineChartView.data = data
}

override open func viewWillAppear(_ animated: Bool) {
self.lineChartView.animate(xAxisDuration: 1.0, yAxisDuration: 1.0)
}
}

@objc(LineChartFormatter)
public class LineChartFormatter: NSObject, IAxisValueFormatter{
var labels: [String] = []

public func stringForValue(_ value: Double, axis: AxisBase?) -> String {
return labels[Int(value)]
}

init(labels: [String]) {
super.init()
self.labels = labels
}
}