Update ruby-test-unit to 3.3.4.
## 3.3.4 - 2019-09-30 {#version-3-3-4}
### Improvements
* Converted markup format to Markdown from RDoc.
[GitHub#164][Patch by OGAWA KenIchi]
* test: Stopped to depend on `Time#inspect` format.
[GitHub#165][Reported by Benoit Daloze]
### Thanks
* OGAWA KenIchi
* Benoit Daloze
## 3.3.3 - 2019-05-10 {#version-3-3-3}
### Fixed
* Fixed a bug that priority mode with test case name that uses
special characters such as `?` can't be used on Windows.
102cf75dbc