broken tco on 6to5

gistfile1.txt

λ node_modules/6to5/bin/6to5-node broken-tco.js
{ yes: 1, '[object Object]': 2, no: 1 }

λ cat node_modules/6to5/package.json | grep version
  "version": "3.5.0",

λ cat broken-tco.js
function format(x) {
  return x.toUpperCase()
}

function makeObj(arr) {
  return arr.reduce(function (obj, x) {
    let upper = format(x)
    obj[x] = 1
    obj[upper] = 2

    return obj
  }, {})
}

let result = makeObj(['yes', 'no'])

console.log(result)