title: ESLint unexpected character '@' for JS decorators
body: <p>I'm trying to use decorators in my JS project, however ESLint is throwing an error stating that the @ symbol is a unexpected character.</p>
  
  <p>My code: </p>
  
  <pre><code>@observable items = [];
  </code></pre>
  
  <p>My .eslintrc:</p>
  
  <pre><code>{
      "parserOptions": {
              "ecmaVersion": 6,
              "ecmaFeatures": {
                  "jsx": true
              },
              "sourceType": "module"
      },
      "env": {
              "browser": true,
              "node": true,
              "es6": false
      },
      "ecmaFeatures": {
              "modules": true
      },
      "rules": {
          "strict": [
              2,
              "global"
          ],
          "quotes": [
              2,
              "single"
          ],
          "indent": [
              2,
              4
          ],
          "eqeqeq": [
              2,
              "smart"
          ],
          "semi": [
              2,
              "always"
          ],
          "max-depth": [
              2,
              4
          ],
          "max-statements": [
              2,
              15
          ],
          "complexity": [
              2,
              5
          ]
      }
  }
  </code></pre>