update cljsjs/react-dom to latest version available

[ekoontz]

Existing version of clsjs/react-dom (16.2.0-3) wasn't available to me, at least on some attempts to fetch via clj -M --main cljs.main --compile hello-world.core --repl (other times I tried, the version was available).

Anyway, the latest release in this change (18.3.1-1) works in my testing, so might as well keep current with it.

To find the latest available release, I looked here: https://clojars.org/cljsjs/react-dom