I've download the latest wekan release and I?ve tried to start it how is described in readme.md

I've exported this environment variable:
NODE_ENV=production
WITH_API=true
MONGO_URL=mongodb://127.0.0.1:27017/wekan
ROOT_URL=http://x.x.x.x:81
PORT=81

then I've typed
root@idea:/usr/src/wekan/bundle# node main.js

obtaining:

/usr/src/wekan/bundle/programs/server/node_modules/fibers/future.js:280
throw(ex);
^

Error: Cannot find module 'node:child_process'
Require stack:

• /usr/src/wekan/bundle/programs/server/boot.js
• /usr/src/wekan/bundle/main.js
  at Function.Module._resolveFilename (internal/modules/cjs/loader.js:1020:15)
  at Function.resolve (internal/modules/cjs/helpers.js:78:19)
  at Object.require (/usr/src/wekan/bundle/programs/server/boot.js:263:34)
  at makeInstallerOptions.fallback (packages/modules-runtime.js:712:18)
  at Module.require (packages/modules-runtime.js:244:14)
  at Module.moduleLink [as link] (/usr/src/wekan/bundle/programs/server/npm/node_modules/meteor/modules/node_modules/@meteorjs/reify/lib/runtime/index.js:52:22)
  at module (models/fileValidation.js:1:126)
  at fileEvaluate (packages/modules-runtime.js:336:7)
  at Module.require (packages/modules-runtime.js:238:14)
  at Module.moduleLink [as link] (/usr/src/wekan/bundle/programs/server/npm/node_modules/meteor/modules/node_modules/@meteorjs/reify/lib/runtime/index.js:52:22)
  at module (models/attachments.js:1:350)
  at fileEvaluate (packages/modules-runtime.js:336:7)
  at Module.require (packages/modules-runtime.js:238:14)
  at Module.moduleLink [as link] (/usr/src/wekan/bundle/programs/server/npm/node_modules/meteor/modules/node_modules/@meteorjs/reify/lib/runtime/index.js:52:22)
  at module (server/publications/attachments.js:1:24)
  at fileEvaluate (packages/modules-runtime.js:336:7)
  at Module.require (packages/modules-runtime.js:238:14)
  at require (packages/modules-runtime.js:258:21)
  at /usr/src/wekan/bundle/programs/server/app/app.js:198362:1
  at /usr/src/wekan/bundle/programs/server/boot.js:385:38
  at Array.forEach ()
  at /usr/src/wekan/bundle/programs/server/boot.js:210:21 {
  code: 'MODULE_NOT_FOUND',
  requireStack: [
  '/usr/src/wekan/bundle/programs/server/boot.js',
  '/usr/src/wekan/bundle/main.js'
  ]
  }