title: Angular2 : concurrent is not recognized as internal or external command
body: <p>While running server for angular2 using npm start is giving error that concurrent is not recognized as internal or external command, why is it happens these kind of error</p>
  
  <p>here is package.json:</p>
  
  <pre><code>{
    "name": "contactlistapp",
    "version": "1.0.0",
    "description": "The app",
    "scripts": {
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "tsc": "./node_modules/.bin/tsc",
      "tsc:w": "./node_modules/.bin/tsc -w",
      "serve": "./node_modules/.bin/live-server --host=localhost --port=3000 .",
      "start": "concurrent \"npm run tsc:w\" \"npm run serve\" "
    },
    "author": "Sarah",
    "license": "ISC",
    "dependencies": {
      "express": "^4.13.3",
      "angular2": "2.0.0-beta.0",
      "systemjs": "0.19.6",
      "es6-promise": "^3.0.2",
      "es6-shim": "^0.33.3",
      "reflect-metadata": "0.1.2",
      "rxjs": "5.0.0-beta.0",
      "zone.js": "0.5.10"
    },
    "devDependencies": {
      "concurrently": "^1.0.0",
      "lite-server": "^1.3.1",
      "typescript": "^1.7.3"
    }
  }
  </code></pre>
  
  <p>structure of the project is there is node_module and typings folder there is app.ts file for server(empty only express is imported), and component.ts(and their .js), tsconfig.json</p>