Issue #4757: fixed a bug of cc.TextFieldTTF that it can't present on Canvas.
Merge branch 'develop-3.0' of https://github.com/cocos2d/cocos2d-html5 into Iss4757_ReleaseAlpha2
Merge pull request #1760 from dingpinglv/Iss4757_ReleaseAlpha2

Issue #4757: fixed a bug of cc.TextFieldTTF that it can't present on Canvas.