fix bug: physics crashes when remove/add children too quick.
Merge pull request #8060 from giuslape/v3

Update Reference plugin-x
[AUTO][ci skip]: updating cocos2dx_files.json
Merge pull request #8570 from CocosRobot/update_cocosfiles_1412732478

[AUTO][ci skip]: updating cocos2dx_files.json
Merge pull request #8209 from boyu0/fix_physics_crash

fix bug: physics crashes when remove/add children too quick.