title: 'super' keyword unexpected inside a generator
body: <p>While trying to use super keyword inside a generator, I'm getting the following error</p>
  
  <pre><code>base_model.js:82
          yield super.$beforeInsert(context);
                ^^^^^
  SyntaxError: 'super' keyword unexpected here
  </code></pre>
  
  <p>Here's the source code (Transpiled via Babel)</p>
  
  <pre><code>class BaseModel extends Model {
      $beforeInsert(context) {
          var _this = this;
  
          return _asyncToGenerator(function* () {
              yield super.$beforeInsert(context);
              if (_this.timestamps) {
                  _this.created_at = new Date();
              }
          })();
      }
  }
  </code></pre>
  
  <p>Here's the original source code</p>
  
  <pre><code>class BaseModel extends Model {
      async $beforeInsert(context) {
          await super.$beforeInsert(context);
          if (this.timestamps) {
              this.created_at = new Date();
          }
      }
  }
  </code></pre>
  
  <p>I'm using node v6.3.1</p>