When I run brunch build --production I see the following warning: warn: config.overrides.production.plugins.babel: perhaps you meant on, off, only, npm

This is what I'm trying to use:

overrides: {
  production: {
    plugins: {
      babel: {
        presets: ['latest', 'babili'],
      },
    },
  },
},

It looks like there is a production-specific overrides schema https://github.com/brunch/brunch/blob/master/lib/utils/config-validate.js so that might be causing issues.