Update ruby-gettext to 3.1.4.

## 3.1.4: 2014-08-26 {#version-3-1-4}

### Improvements

  * Improved document markups by Markdown.
    [GitHub#33] [Patch by Masafumi Yokoyama]

### Fixes

  * `GetText::Tools::Task`: Fixed a bug that `Errno::ENOENT: No such
    file or directory @ rb_file_s_mtime - doc/po/ja/rroonga.edit.po`
    like error is occurred.
  * `GetText::Tools::Task`: Fixed markup in document.

### Thanks

  * Masafumi Yokoyama

## 3.1.3: 2014-07-13 {#version-3-1-3}

### Improvements

  * Supported `Pathname` in `$LOAD_PATH`.
    [GitHub#32] [Patch by Ben Carlsson]
  * `GetText::Tools::Task`: Added `msgcat_options` to custom `rmsgcat`
    command line.
  * `GetText::Tools::Task`: Migrated to `.edit.po` style.
  * `GetText::Tools::Task`: Added `pot_creator` to custom POT creation.
  * `rmsgcat`: Added `--no-translator-comment` option.
  * `rmsgcat`: Added `--no-extracted-comment` option.
  * `rmsgcat`: Added `--no-flag-comment` option.
  * `rmsgcat`: Added `--no-previous-comment` option.

### Fixes

  * `rmsgmerge`: Fixed a bug that metadata in fuzzy message aren't merged.

### Thanks

  * Ben Carlsson

(obache)