Polyfill approach

[cfarm]

Adding this here to note for future updates to our standards addressing polyfills - useful link from @sephcoster in chat

Used some practices in this article that were quite helpful - only adds polyfill on detection of missing methods and is also non-blocking which is nice.
https://philipwalton.com/articles/loading-polyfills-only-when-needed/

[anselmbradford]

We don't currently automatically add polyfills in consumerfinance.gov. We manually add them.