title: ESLint: First instance of let results in "unexpected token" error
body: <p>My javascript:</p>
  
  <pre><code>let foo = 'bar'
  </code></pre>
  
  <p>Why does ESLint respond with the following?</p>
  
  <pre><code>~/index.js
    1:5  error  Parsing error: Unexpected token foo
  
  ✖ 1 problem (1 error, 0 warnings)
  </code></pre>
  
  <p>It seems like no matter where in the script, the first instance of using let to set a variable gets this error. Why??</p>
  
  <p>My .eslintrc file:</p>
  
  <pre><code>module.exports = {
      "env": {
          "node": true
      },
      "extends": "eslint:recommended",
      "rules": {
          "indent": [
              "error",
              "tab"
          ],
          "linebreak-style": [
              "error",
              "unix"
          ],
          "quotes": [
              "error",
              "single"
          ],
          "semi": [
              "error",
              "never"
          ]
      }
  };
  </code></pre>