care for multibyte characters

The size method counts multibyte character as "1".
So as we use multibyte character, the tail of maintenance.html is trimmed.
![screen shot 2014-09-04 at 21 15 06](https://cloud.githubusercontent.com/assets/2055516/4148913/48bece74-342d-11e4-896b-70829e9a41f4.png)