Fix link to Crown Copyright

We were pointing to a 404. This address matches what's in the Design System [1].

[1] https://design-system.service.gov.uk/components/footer/

config/locales/en.yml

@@ -87,7 +87,7 @@ en:
       statistics: Statistics
       worldwide: Worldwide
     layout_footer:
-      copyright_html: <a class="govuk-footer__link govuk-footer__copyright-logo" href="http://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/copyright-and-re-use/crown-copyright/">© Crown copyright</a>
+      copyright_html: <a class="govuk-footer__link govuk-footer__copyright-logo" href="https://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/uk-government-licensing-framework/crown-copyright/">© Crown copyright</a>
       licence_html: All content is available under the <a class="govuk-footer__link" href="https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/" rel="license">Open Government Licence v3.0</a>, except where otherwise stated
       support_links: Support links
     layout_for_public: