dapp-treasury is failing CI on Agoric SDK master

[michaelfig]

Describe the bug

dapp-treasury is failing CI https://github.com/Agoric/agoric-sdk/runs/6886341599?check_suite_focus=true#step:11:21 says:

> @agoric/dapp-treasury-ui
$ yarn build:ses && yarn build:react
$ cp ../node_modules/ses/dist/lockdown.umd.js public/
$ react-scripts build
Creating an optimized production build...
Browserslist: caniuse-lite is outdated. Please run:
npx browserslist@latest --update-db
Why you should do it regularly:
https://github.com/browserslist/browserslist#browsers-data-updating
Failed to compile.
/home/runner/work/agoric-sdk/agoric-sdk/agoric-sdk/packages/casting/src/defaults.js 36:56
Module parse failed: Identifier directly after number (36:56)
File was processed with these loaders:
 * ../node_modules/react-scripts/node_modules/babel-loader/lib/index.js
You may need an additional loader to handle the result of these loaders.
|  */
| 
> export const exponentialBackoff = (attempt = 0, base = 1_000, cap = 30_000) => {
|   return randomBackoff(2 ** attempt * base, cap);
| };
error Command failed with exit code 1.

We apparently need to upgrade react-scripts in that package.

To Reproduce

Run CI on any branch based off current master.

Expected behavior

Clean CI run.

Platform Environment

• what OS are you using? what version of Node.js?
• is there anything special/unusual about your platform?
• what version of the Agoric-SDK are you using? (run git describe --tags --always)

Additional context

Add any other context about the problem here.

Screenshots

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