This updates Elements to use the details polyfill from there instead.
What problem does the pull request solve?
If you npm install the gov template, the toolkit and elements (govuk-elements-sass), the expectation is that you should have everything you need to use the gov styles. However, the element polyfill is missing since govuk-elements-sass only includes the sass.
The details polyfill has been copied to the frontend toolkit and released as v7.1.0.
This updates Elements to use the details polyfill from there instead.
What problem does the pull request solve?
Raised in issue https://github.com/alphagov/govuk_elements/issues/400
How has this been tested?
I ran Elements locally and ensured that the details polyfill was loading correctly from Frontend Toolkit.
I tested that the details/summary elements worked as expected in Firefox 48 using Browserstack.
Screenshots (if appropriate):
What type of change is it?
Has the documentation been updated?