fixed #1056 The bug of cc.ProgressTimer has fixed that Midpoint is wrong on Canvas Mode.
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss1056_FixProgressAnchorPointBug
Merge pull request #1059 from dingpinglv/Iss1056_FixProgressAnchorPointBug

fixed #1056 The bug of cc.ProgressTimer has fixed that Midpoint is wrong on Canvas Mode.