npm: fix compatibility with `create-urbit-app`
The version of babel/webpack/everything bundled with CRA is limited
in its ES features. Reducing to ES2017 let it work by default.
"outDir": "./dist",
"module": "ES2020",
"noImplicitAny": true,
- "target": "ES2020",
+ "target": "ES2017",
"pretty": true,
"moduleResolution": "node",
"esModuleInterop": true,
