rosjava_bootstrap: 0.1.20-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `rosjava_bootstrap` to `0.1.20-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.1`
- previous version for package: `0.1.19-0`

## rosjava_bootstrap

```
* Trim maven repository list and backup with maven central.
* Contributors: Daniel Stonier
```