Example app is broken

[johngrimes]

Following the change in #29, the example app seems to be broken:

➜ npm run build -w apps/ecl-builder-app

> ecl-builder-app@0.1.0 build
> react-scripts build

Creating an optimized production build...
Failed to compile.

Error: [BABEL] /Users/gri306/Code/ecl-builder/apps/ecl-builder-app/src/index.tsx: Cannot find module '@babel/plugin-proposal-private-property-in-object'
Require stack:
- /Users/gri306/Code/ecl-builder/node_modules/babel-preset-react-app/create.js
- /Users/gri306/Code/ecl-builder/node_modules/babel-preset-react-app/index.js
- /Users/gri306/Code/ecl-builder/node_modules/@babel/core/lib/config/files/module-types.js
- /Users/gri306/Code/ecl-builder/node_modules/@babel/core/lib/config/files/configuration.js
- /Users/gri306/Code/ecl-builder/node_modules/@babel/core/lib/config/files/index.js
- /Users/gri306/Code/ecl-builder/node_modules/@babel/core/lib/index.js
- /Users/gri306/Code/ecl-builder/node_modules/@rollup/plugin-babel/dist/index.js
- /Users/gri306/Code/ecl-builder/node_modules/workbox-build/build/lib/bundle.js
- /Users/gri306/Code/ecl-builder/node_modules/workbox-webpack-plugin/build/generate-sw.js
- /Users/gri306/Code/ecl-builder/node_modules/workbox-webpack-plugin/build/index.js
- /Users/gri306/Code/ecl-builder/node_modules/react-scripts/config/webpack.config.js
- /Users/gri306/Code/ecl-builder/node_modules/react-scripts/scripts/build.js (While processing: "/Users/gri306/Code/ecl-builder/node_modules/babel-preset-react-app/index.js")
    at Generator.next (<anonymous>)
    at Generator.next (<anonymous>)
    at Generator.next (<anonymous>)
    at Generator.next (<anonymous>)
    at cachedFunction.next (<anonymous>)
    at loadPresetDescriptor.next (<anonymous>)
    at recursePresetDescriptors.next (<anonymous>)
    at Generator.next (<anonymous>)
    at loadFullConfig.next (<anonymous>)
    at transform.next (<anonymous>)

npm ERR! Lifecycle script `build` failed with error: 
npm ERR! Error: command failed 
npm ERR!   in workspace: ecl-builder-app@0.1.0 
npm ERR!   at location: /Users/gri306/Code/ecl-builder/apps/ecl-builder-app