hrpsys: 315.1.8-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `hrpsys` to `315.1.8-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.2`
- previous version for package: `315.1.7-0`

## hrpsys

```
* Do not pollute src directory, https://github.com/start-jsk/hrpsys/issues/3
* Utilize .travis.yml
* Initial commit of CHANGELOG.rst
* Contributors: Kei Okada, Atsushi Tsuda, Isaac Isao Saito, chen.jsk, Ryohei Ueda, Iori Kumagai, Manabu Saito, Takuya Nakaoka, Shunichi Nozawa, Yohei Kakiuchi
```