Rollup issue

index.mjs

console.log("Hello World");

package.json

{ 
  "name": "fail-rollup",
  "version": "1.0.0",
  "main": "index.mjs",
  "out":"index.umd.js",
  "license": "ISC",
  "devDependencies": {
    "rollup": "2.1.0"
  }
}

rollup.config.mjs

import pkg from './package.json';
  
const build = {
  input: pkg.main,
  output:[
    {
      name:'test',
      file:pkg.out,
      format:'umd'
    }
  ]
}
export default [build]