title: JSX not allowed in files with extension ' .js' with eslint-config-airbnb
body: <p>I've installed <a href="https://github.com/airbnb/javascript/tree/master/packages/eslint-config-airbnb" rel="noreferrer">eslint-config-airbnb</a> that is supposed to pre configure ESLINT for React:</p>
  
  <blockquote>
    <p>Our default export contains all of our ESLint rules, including
    ECMAScript 6+ and React. It requires eslint, eslint-plugin-import,
    eslint-plugin-react, and eslint-plugin-jsx-a11y.</p>
  </blockquote>
  
  <p>My <code>.eslintrc</code> extending its configuration:</p>
  
  <pre><code>{ "extends": "eslint-config-airbnb",
    "env": {
      "browser": true,
      "node": true,
      "mocha": true
    },
    "rules": {
      "new-cap": [2, { "capIsNewExceptions": ["List", "Map", "Set"] }],
      "react/no-multi-comp": 0,
      "import/default": 0,
      "import/no-duplicates": 0,
      "import/named": 0,
      "import/namespace": 0,
      "import/no-unresolved": 0,
      "import/no-named-as-default": 2,
      "comma-dangle": 0,  // not sure why airbnb turned this on. gross!
      "indent": [2, 2, {"SwitchCase": 1}],
      "no-console": 0,
      "no-alert": 0,
      "linebreak-style": 0
    },
    "plugins": [
      "react", "import"
    ],
    "settings": {
      "import/parser": "babel-eslint",
      "import/resolve": {
        "moduleDirectory": ["node_modules", "src"]
      }
    },
    "globals": {
      "__DEVELOPMENT__": true,
      "__CLIENT__": true,
      "__SERVER__": true,
      "__DISABLE_SSR__": true,
      "__DEVTOOLS__": true,
      "socket": true,
      "webpackIsomorphicTools": true
    }
  }
  </code></pre>
  
  <p>Unfortunatelly I'm getting the following error when linting a .js file with React JSX code inside it:</p>
  
  <pre><code> error  JSX not allowed in files with extension '.js'              react/jsx-filename-extension
  </code></pre>
  
  <p>Wasn't eslint-config-airbnb configured react to support JSX already, as stated ? </p>
  
  <p>What should be done to remove that error ?</p>