title: Eslint: remove keyword function
body: <p>I was wondering if there is a rule or a way to flag function declarations as an error in favor of arrow functions. As an example:</p>
  
  <pre><code>// error
   function foo() {
     return "bar"
   }
  
  //acceptable
   const foo = () =&gt; "bar"
  </code></pre>
  
  <p>its pretty simple, but I haven't been able to find any rules or packages.</p>