es6 linting bug: destructuring named parameters with default values

[keithriver]

Test executes and passes successfully, but linter gives warning message:

Expected "," and instead saw "="
Expected an identifier and instead saw "0"

on lines with constructor parameters.

   describe('es6 parameters', function() {  
        it('constructor destructuring optional object with default values', function() {
    
            class Vector {
                constructor ({x = 0, y = 0} = {}) {
                  this.x = x
                  this.y = y
                }
            }
  
            class VisibleObject extends Vector {
              constructor ({x = 0, y = 0, opacity = 1} = {}) {
                  super({x, y})
                  this.opacity = opacity
                }
            }

            let vo1 = new VisibleObject({x: 10, y: 15})
            let vo2 = new VisibleObject()
    
            assert.equal(co1.x, 10);
            assert.equal(co1.y, 15);
            assert.equal(co1.opacity, 1);
            assert.equal(co2.x, 0);
            assert.equal(co2.y, 0);
            assert.equal(co2.opacity, 1);
        });
    });