frontier_exploration: 0.2.1-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `frontier_exploration` to `0.2.1-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.4`
- previous version for package: `0.2.0-0`

## frontier_exploration

```
* Update example launch files
* Update package.xml
* Contributors: Paul Bovbel
```