Fix utf-8-mac problem in grunt translation task

![concrete5____](https://cloud.githubusercontent.com/assets/514294/2811070/ff279782-ce01-11e3-8110-d28cfe94f68b.png)

Translated string should be "多言語サポート設定", but a first string is broken.
This is not a Japanese only problem, some other languages has same problem.

A blog post about this problem: http://me.dt.in.th/page/StringDecoder/