fix(invite): check Toolbox render method error

The app will crash for me with react complaining about not a component
being passed.

react/features/invite/components/index.js

 export { default as AddPeopleDialog } from './AddPeopleDialog';
 export { default as InfoDialogButton } from './InfoDialogButton';
+export { default as InviteButton } from './InviteButton';
 export { DialInSummary } from './dial-in-summary';