When update title of a button node, need to get title node via setter (#3167)
When update title of a button node, need to get title node via setter (#3167)

* When update title of a button node, need to get title node via setter

* Explain why we need to call self.titleNode

* Fix previous comment

flovouin/AsyncDisplayKit,flovouin/AsyncDisplayKit,maicki/AsyncDisplayKit,maicki/AsyncDisplayKit,maicki/AsyncDisplayKit,flovouin/AsyncDisplayKit,maicki/AsyncDisplayKit,flovouin/AsyncDisplayKit,maicki/AsyncDisplayKit,flovouin/AsyncDisplayKit