Describe the bug

b-table sorting does not work with data of the following format: "2020-12-03T13:27:42+01:00"

Steps to reproduce the bug

<b-table 
    :items="[{createdOn: '2020-12-03T13:27:42+01:00'}, {createdOn: '2020-12-03T13:26:39+01:00'}]"
    :fields="[{key: 'createdOn', sortable: true}]"></b-table>

Expected behavior

Since the data are strings, it should be sorted.

Versions

Libraries:

• BootstrapVue: 2.20.0, 2.20.1
• Bootstrap: NA
• Vue: 2.6.12

Environment:

NA

Demo link

https://jsfiddle.net/5yex9u1f/

Additional context

This works fine on bootstrap-vue 2.19
see https://jsfiddle.net/bf6r1Lx4/

I think the issue was introduced with #6105