Iterate polyfills instead of calling each individually

[dgreif]

While reviewing #4, I noticed we are repeating these function calls for each polyfill. If we put all the polyfills in an array and iterate, we can achieve the same goal with a lot less code. It also helps avoid accidentally adding a new polyfill to one of these functions while missing one of the others

This takes the lib/index.js from 2,855 bytes to 2,311 bytes. Roughly .5kB before minification/gzip isn't a ton, but it's something 😄