upgrade minimum nodejs version, yarn dev deps

Looks like I basically had to do this to keep up. With nodejs version 12
(current LTS), the version of fsevents I installed wouldn't build. A
"yarn upgrade" by itself resulted in a new problem as described in #69.
Conversely, the new versions don't install with nodejs 8. So I bit the
bullet and upgraded all the dev dependency stuff and the nodejs at once.
nodejs 10 seems capable of running either the old or new, fwiw.

I'm a little sad that this seems to have made the UI bundle 5% larger.
Before, "yarn build" said 350 KiB. After, 369 KiB. A little bit in
several places. For example, jquery-ui.bundle.js went from 156 KiB (in
2 chunks) to 160 KiB (in 1 chunk) for some reason.

scripts/script-functions.sh

@@ -37,7 +37,7 @@ fi
 
 # Useful constants
 #
-NODE_MIN_VERSION="8"
+NODE_MIN_VERSION="10"
 YARN_MIN_VERSION="1.0"
 CARGO_MIN_VERSION="0.2"
 RUSTC_MIN_VERSION="1.40"