[Pivot][Accessibility] Focus border issue

[ankitk94]

Bug Report

• Package version(s): 4.35.1002
• Browser and OS versions: Edge

Describe the issue:

Pivot focus border not behaving as expected

Actual behavior:

High contrast:

Normal mode:

Border incomplete for "Bar".

If applicable, please provide a codepen repro:

Official site (https://dev.office.com/fabric#/components/pivot)