{
  "name": "threeflows",
  "version": "0.1.0",
  "engines": {
    "node": "5.9.1"
  },
  "main": "server/index.js",
  "scripts": {
    "start": "node server/index.js",
    "watch": "cd ui && npm run watch && cd ..",
    "heroku-postbuild": "cd ui && npm run build && cd .."
  },
  "dependencies": {
    "body-parser": "^1.15.1",
    "express": "4.13.3",
    "lodash": "^4.13.1",
    "pg": "^5.1.0"
  },
  "keywords": [],
  "license": "MIT"
}

{
  "name": "threeflows",
  "version": "0.1.0",
  "engines": {
    "node": "5.9.1"
  },
  "main": "server/index.js",
  "scripts": {
    "start": "node server/index.js",
    "watch": "cd ui && npm run watch && cd ..",
    "heroku-postbuild": "cd ui && mkdir build && npm run build && cd .."
  },
  "dependencies": {
    "body-parser": "^1.15.1",
    "express": "4.13.3",
    "lodash": "^4.13.1",
    "pg": "^5.1.0"
  },
  "keywords": [],
  "license": "MIT"
}

Add postbuild step to create build folder
Add postbuild step to create build folder
