Log Message:
Update ruby-test-unit to 3.2.1.

## 3.2.1 - 2016-07-19 {#version-3-2-1}

### Improvements

  * Clarified lib/test/unit/diff.rb license. It's a triple license of
    the Ruby license, PSF license and LGPLv2.1 or later.
    [Reported by Luisa Pace]

  * Reported norification when data driven test doesn't have
    parameter.
    [GitHub#122][Reported by Satoshi "Moris" Tagomori]

### Thanks

  * Luisa Pace

  * Satoshi "Moris" Tagomori

## 3.2.0 - 2016-06-12 {#version-3-2-0}

### Improvements

  * Supported rxvt family terminals as color available terminals.
    [GitHub#121][Reported by Ippei Kishida]

### Thanks

  * Ippei Kishida

## 3.1.9 - 2016-05-20 {#version-3-1-9}

### Fixes

  * Fixed conflict with test-unit-power_assert.
    [GitHub#120][Patch by Kazuki Tsujimoto]

  * Fixed a bug that path in `$LOAD_PATH` may be removed.

### Thanks

  * Kazuki Tsujimoto

## 3.1.8 - 2016-03-19 {#version-3-1-8}

### Improvements

  * Added `--stop-on-failure` command line option. With this option,
    running test suite is stopped immediately when one test is failed
    or an error is raised in one test.