openhrp3: 3.1.5-4 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `openhrp3` to `3.1.5-4`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.1`
- previous version for package: `3.1.5-3`

## openhrp3

```
* Fix to an issue that caused https://github.com/start-jsk/hrpsys/issues/25
* Initial commit of CHANGELOG.rst
* Contributors: Kei Okada, chen.jsk, Ryohei Ueda, Isaac Isao Saito, Hiroyuki Mikita, Iori Kumagai, Takuya Nakaoka, Shunichi Nozawa, Rosen Diankov, Yohei Kakiuchi
```