title: Prevent use of unsupported JavaScript features in IE11 using ESLint?
body: <p>I have an existing ESLint configuration with "ecmaVersion" set to "5" that I want to modify to allow the use of <strong>let</strong> and <strong>const</strong> which are ES6 features. There are mostly* supported in Internet Explorer 11. However, I want to reject the use of any ES6 features that aren't supported in IE11, e.g. classes. How can I do that with ESLint?</p>
  
  <p>I did find the <em>eslint-plugin-ie11</em> plug-in, but it only covers a few unsupported features.</p>
  
  <p>*I would also like to block the use of let in loops, which is not supported in IE11.</p>