fix compilation error, sorry :) (#2070)

ios/RCCTabBarController.m

@@ -266,7 +266,7 @@
         NSString *badgeColor = actionParams[@"badgeColor"];
         UIColor *color = badgeColor != (id)[NSNull null] ? [RCTConvert UIColor:badgeColor] : nil;
         
-        if (viewController.tabBarItem respondsToSelector:@selector(badgeColor)) {
+        if ([viewController.tabBarItem respondsToSelector:@selector(badgeColor)]) {
           viewController.tabBarItem.badgeColor = color;
         }
         viewController.tabBarItem.badgeValue = [NSString stringWithFormat:@"%@", badge];