Wrong number of label on X axis of line chart when there is only one data entry

Every thing works fine with line chart when I have more than one data entry. However, when I only have one data entry, something wrong with the label of x axis.

What I want is only show one label and align it to the data point.
I've tried the setting below but none of them work.
`chartView.xAxis.granularityEnabled = true`
`chartView.xAxis.granularity = 1`
`chartView.xAxis.setLabelCount(1, force: true)`

I've also tried to set minimum and maximum value of x axis with -1 to 1, 0 to 1, and even 0 to 0. But still didn't work :(
Is there any way to correctly show the label?

## Charts Environment
Charts version/Branch/Commit Number: 3.1.1
Xcode version: 9.2
Swift version: 4.0
Platform(s) running Charts: iOS
macOS version running Xcode: 10.2.6

No source file or test is named. Reproduce the issue with a one-entry line chart on iOS, then trace the x-axis label generation and compare it with a chart containing multiple entries. Done means exactly one x-axis label is shown and aligned with the data point.

Written by the indexing model from the issue text.