Log Message:
Update ruby-test-unit to 3.2.4.

## 3.2.4 - 2017-05-23 {#version-3-2-4}

### Improvements

  * Updated tests for Ruby 2.4. [GitHUb#136][Patch by Kazuki Tsujimoto]

  * Supported power\_assert 1.0.0. [GitHub#137][Patch by Kazuki Tsujimoto]

  * Added the getting started document.
    [GitHub#139][GitHub#141][Patch by Hiroyuki Sato]

  * Added the document for `attribute`.
    [GitHub#143][Patch by Fumiaki MATSUSHIMA]

  * Improved a link for GitHub. [GitHub#144][Patch by rochefort]

  * Updated `.travis.yml`. [GitHub#145][Patch by Jun Aruga]

### Fixes

  * Fixed a contributor name. [GitHub#131][Patch by Akira Matsuda]

  * Fixed typos in document. [GitHub#132][Patch by Akira Matsuda]

  * Fixed typos in document. [GitHub#134][Patch by Yuji Yaginuma]

  * Fixed a bug that data label with "(" isn't supported.
    [GitHub#135][Reported by Kazuki Tsujimoto]

  * Fixed assertion message in English.
    [GitHub#133][Reported by Khalil Fazal]

  * Fixed a typo in typo fix. [GitHub#138][Patch by kami]

  * Fixed a bug that target location finder may return wrong
    location. [GitHub#146][Patch by Yuki Ito]

  * Fixed a bug that `--no-show-detail-immediately` raises an error.
    [GitHub#147][Reported by MSP-Greg]

### Thanks

  * Akira Matsuda

  * Yuji Yaginuma

  * Kazuki Tsujimoto

  * Khalil Fazal

  * kami

  * Hiroyuki Sato

  * Fumiaki MATSUSHIMA

  * rochefort

  * Jun Aruga

  * Yuki Ito

  * MSP-Greg