update to v2.2.0 of nhsuk-frontend including new favicons

[chrimesdev]

Description

Version 2.2.0 of the NHS.UK frontend library has been released, which includes new favicon styling and recommended favicons to use.

Related issue

Checklist

• [x] Tested against the NHS.UK frontend testing policy (Resolution, Browser & Accessibility)
• [x] Code follows the NHS.UK frontend coding standards
• [x] Documentation
• [x] Version number increase (using SEMVER)
• [x] CHANGELOG entry
• [ ] Validated on staging environment (only required for releases)