We like to aim for trailing commas in code when possible, and tend to

write new code this way. However, we've have had a lot of legacy

JavaScript code (which wasn't comma-safe) that was ported to ES6, but

still lacked commas.
This change updates all ES6 code to use trailing commas.
This helps satisfy ESLint.

Verified that ESLint no longer had complaints about trailing commas.