Delete comma from popover

Summary: Looks like this got accidentally added here: https://our.intern.facebook.com/intern/diff/D18397950/

Reviewed By: mweststrate

Differential Revision: D18779992

fbshipit-source-id: 7a61cda4a9a4287ebc56acb5d2b85fce8e3381e3

src/ui/components/Popover.tsx

@@ -104,7 +104,6 @@ export default class Popover extends PureComponent<Props> {
           opts={this.props.forceOpts || {}}>
           {this.props.children}
         </PopoverContainer>
-        ,
       </>
     );
   }