octomap_ros: 0.3.1-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `octomap_ros` to `0.3.1-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.2`
- previous version for package: `0.3.0-0`

## octomap_ros

```
* Fixing #3 <https://github.com/OctoMap/octomap_ros/issues/3> (explicit instantiation in conversions.cpp)
```