2.0-preview readme needs to reference using slot instead of class to define the trigger

[mbinette]

The documentation states

<paper-menu-button>
  <paper-icon-button icon="menu" class="dropdown-trigger"></paper-icon-button>
  ...
</paper-menu-button>

The 2.0-preview code no longer uses the class="dropdown-trigger". Instead, it should be changed to slot="dropdown-trigger"

[masonlouchart]

Done here 99036ed?

[mbinette]

Yes, fixed.