Remove bottom tab badge when calling setTabBadge with empty object (#668)

src/deprecated/platformSpecificDeprecated.android.js

 }
 
 function navigatorSetTabBadge(navigator, params) {
-  const badge = params.badge.toString();
+  const badge = params.badge ? params.badge.toString() : '';
   if (params.tabIndex >= 0) {
     newPlatformSpecific.setBottomTabBadgeByIndex(params.tabIndex, badge);
   } else {