[iOS] Don't bring the packager to the foreground upon launch

ios/scripts/run-packager.sh

       exit 2
     fi
   else
-    open "$SRCROOT/../../node_modules/react-native/packager/launchPackager.command" || echo "Can't start packager automatically"
+    open -g "$SRCROOT/../../node_modules/react-native/packager/launchPackager.command" || echo "Can't start packager automatically"
   fi
 fi