title: mobx + react unexpected token
body: <p>so i created an app with react without configuration from <a href="https://facebook.github.io/react/blog/2016/07/22/create-apps-with-no-configuration.html" rel="noreferrer">https://facebook.github.io/react/blog/2016/07/22/create-apps-with-no-configuration.html</a></p>
  
  <p>I installed mobx and mobx-react ,but is still shows the error of unexpected token before @ symb.</p>
  
  <p>Do I need to add something else, or my current configuration is wrong ?:(</p>
  
  <p>package.json</p>
  
  <pre><code>"devDependencies": {
  "react-scripts": "0.8.4",
  "babel-core": "^6.7.6",
  "babel-loader": "^6.2.4",
  "babel-preset-es2015": "^6.6.0",
  "babel-preset-react": "^6.5.0",
  "babel-preset-stage-0": "^6.5.0"
  },
  "dependencies": {
  "autobind-decorator": "^1.3.4",
  "classnames": "^2.2.5",
  "lodash": "^4.15.0",
  "mobx": "^2.5.1",
  "mobx-react": "^3.5.5",
  "react": "^15.3.1",
  "react-dom": "^15.3.1",
  "validator": "^5.6.0"
   },
  </code></pre>
  
  <p>.babelrc</p>
  
  <pre><code>{
    "presets": ["es2015", "stage-0", "react"],
    "plugins": [
        "transform-decorators-legacy",
        "transform-class-properties"
    ]
  }
  </code></pre>
  
  <p>And the code</p>
  
  <pre><code>import React, { Component } from 'react';
  import { action, observable } from 'mobx'
  import {observer} from 'mobx-react';
  
  
  class App {
      @observer cake = [];
  }
  
  export default new App();
  </code></pre>