cob_extern: 0.5.2-4 in 'hydro/distribution.yaml' [bloom]

Increasing version of package(s) in repository `cob_extern` to `0.5.2-4`:

- distro file: `hydro/distribution.yaml`
- bloom version: `0.5.2`
- previous version for package: `0.5.2-3`

## cob_extern

```
* Merge branch 'hydro_dev' into hydro_release_candidate
* Update package.xml
* Contributors: Florian Weißhardt, ipa-fmw
```

## libntcan

```
* Add missing find_package calls
* Contributors: Scott K Logan
```

## libpcan

```
* Add missing rospack depends
* Add missing find_package calls
* Contributors: Scott K Logan
```

## libphidgets

```
* Add missing rospack depends
* Add missing find_package calls
* Contributors: Scott K Logan
```