Overview of the problem

Buefy version: [0.8.20]
Vuejs version: [2.6.11]
OS/Browser: Windows 10/Chrome 83.0.4103.116

Description

customSort function is not called when sortMultiple is enabled on a Table.

Steps to reproduce

1. Create a Table with sortMultiple
2. Create a column with a customSort function
3. Try to sort that column and see if the customSort function gets called

Expected behavior

Table column should be sorted using the customSort function.

Actual behavior

The column does not get sorting at all and the row order remains unchanged. No errors are reported on the console.