Update ruby-gettext to 2.3.9.

## 2.3.9: 2013-04-21

This is a msgmerge updated release.

### Improvements

  * [tools] Used the more modern word "cannot" instead of "can
    not". [GitHub #15] [Patch by Benjamin Kerensa]
  * Cleared license descriptions. [Suggested by J辿r辿my Bobbio]

### Fixes

  * Avoided including native extentions in this gem for Windows users.

### Thanks

  * Benjamin Kerensa
  * J辿r辿my Bobbio

## 2.3.8: 2013-04-05

This is a msgmerge improved release.

### Improvements

  * Added licence information to the gemspec.
    [GitHub #13] [Patch by jordimassaguerpla]
  * Supported Ruby 2.0.0.
    [GitHub #14] [Reported by mtasaka]

### Fixes

  * [rxgettext] Fixed a bug that the comment for the previous message
    also exists in the current message.
    [Debian #684184] [Reported by Francesco Poli] [Patch by J辿r辿my Bobbio]

### Thanks

  * jordimassaguerpla
  * mtasaka
  * Francesco Poli
  * J辿r辿my Bobbio

(obache)