message: Show `core` apiGroup in resource dropdown
  Fixes
diff: @@ -44,7 +44,7 @@ const DropdownItem: React.SFC<DropdownItemProps> = ({model, showGroup}) => <Reac
  <ResourceIcon kind={model.kind} />
  </span>
  {model.kind}
  - {showGroup && <React.Fragment>&nbsp;<small className="text-muted">&ndash; {model.apiGroup}/{model.apiVersion}</small></React.Fragment>}
  + {showGroup && <React.Fragment>&nbsp;<small className="text-muted">&ndash; {model.apiGroup || 'core'}/{model.apiVersion}</small></React.Fragment>}
  </React.Fragment>;
  const ResourceListDropdown_: React.SFC<ResourceListDropdownProps> = props => {
  