Fixed #3825: modify SimpleAudioEngine's _maxAudioInstance to 5
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3825_SimpleAudioEngine
Merge pull request #1526 from dingpinglv/Iss3825_SimpleAudioEngine

Fixed #3825: modify SimpleAudioEngine's _maxAudioInstance to 5