rosjava_bootstrap: 0.1.21-0 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `rosjava_bootstrap` to `0.1.21-0`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.9`
- previous version for package: `0.1.20-1`

## rosjava_bootstrap

```
* Android gradle plugin 0.9.+->0.11.+ (studio 0.6)
* Android sdk build tools 19.0.3 -> 19.1 (studio 0.6)
* Contributors: Daniel Stonier
```