Add debian package dependency for new packaging dependency. (#698)

This was introduced in #693 and I realized that it needed the stdeb
dependency while I was on a walk but forgot to add that before
re-reviewing and merging that PR.

This package is available for Python 2 in
[Buster](https://packages.debian.org/buster/python3-packaging) and
[Bionic](https://packages.ubuntu.com/bionic/python-packaging).

As well as for Python 3 in
[Buster](https://packages.debian.org/buster/python3-packaging) and
[Bionic](https://packages.ubuntu.com/bionic/python3-packaging) and later
distributions.

stdeb.cfg

@@ -1,8 +1,8 @@
 [DEFAULT]
 ; release with a high debinc to avoid conflict with upstream debian of the same release version
 Debian-Version: 100
-Depends: python-yaml, python-empy, python-argparse, python-rosdep (>= 0.15.0), python-rosdistro (>= 0.8.0), python-vcstools (>= 0.1.22), python-setuptools, python-catkin-pkg (>= 0.4.3)
-Depends3: python3-yaml, python3-empy, python3-rosdep (>= 0.15.0), python3-rosdistro (>= 0.8.0), python3-vcstools (>= 0.1.22), python3-setuptools, python3-catkin-pkg (>= 0.4.3)
+Depends: python-yaml, python-empy, python-argparse, python-packaging, python-rosdep (>= 0.15.0), python-rosdistro (>= 0.8.0), python-vcstools (>= 0.1.22), python-setuptools, python-catkin-pkg (>= 0.4.3)
+Depends3: python3-yaml, python3-empy, python3-packaging, python3-rosdep (>= 0.15.0), python3-rosdistro (>= 0.8.0), python3-vcstools (>= 0.1.22), python3-setuptools, python3-catkin-pkg (>= 0.4.3)
 Conflicts: python3-bloom
 Conflicts3: python-bloom
 Copyright-File: LICENSE.txt