Fixed #5781: correct a bug of cc.WebAudio that sourceNode's playbackState is invalid
Merge branch 'develop' of git://github.com/cocos2d/cocos2d-html5 into Iss5781_ReleaseV3rc2
Merge pull request #2062 from dingpinglv/Iss5781_ReleaseV3rc2

Fixed #5781: correct a bug of cc.WebAudio that sourceNode's playbackState is invalid