Describe the bug
Sorting of series is not working properly in legend

To Reproduce
Steps to reproduce the behavior:

1. Create a chart (use the TSVB as an example)
2. Group it by terms (select small amount of terms, that needed for rendering the same labels)
3. Choose an another type of sorting (descending -> ascending)
4. See that colors of series shuffled in different way in the legend, but labels stayed on the same position

Expected behavior
Labels should also change its position

Screenshots

Version (please complete the following information):

• OS: Windows 10
• Browser Chrome 73
• Elastic Charts: 3.4.4

Additional context
Add any other context about the problem here.

Errors in browser console
If applicable, add any console error.

Kibana Cross Issues
Add any Kibana related issues here.

Checklist

• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present