{
    ...
    "scripts": {
      "start": "./node_modules/.bin/nodemon ./node_modules/.bin/babel-node .",
      "prepublish": "npm run build",
      "test": "ava test",
      "build": "babel src -d dist"
    },

    "ava": {
      "babel": "inherit"
    },
    "devDependencies": {
      "@babel/cli": "^7.0.0",
      "@babel/core": "^7.0.0",
      "@babel/node": "^7.0.0",
      "@babel/preset-env": "^7.0.0",
      "@babel/register": "^7.0.0",
      "nodemon": "^1.12.1"
    },
    "dependencies": {
      "@babel/core": "^7.3.3",
      "@babel/plugin-proposal-class-properties": "^7.3.3",
      "@babel/plugin-proposal-json-strings": "^7.2.0",
      "@babel/plugin-syntax-dynamic-import": "^7.2.0",
      "@babel/plugin-syntax-import-meta": "^7.2.0",
      "@babel/preset-env": "^7.0.0",
      "babel-polyfill": "^6.26.0",
      "dotenv": "^6.2.0",
      "excel": "^1.0.0",
      "mysql": "^2.16.0",
      "npm": "^6.8.0"
    }
  }

Error: Cannot find module 'babel-polyfill'