Tell stdeb not to make Python 2 packages (#379)

Fixes 3e2235c

Author: cottsay

stdeb.cfg

@@ -1,4 +1,5 @@
 [catkin_pkg]
+No-Python2:
 Debian-Version: 100
 ; catkin-pkg-modules same version as in:
 ; - setup.py
@@ -11,6 +12,7 @@ X-Python3-Version: >= 3.6
 Setup-Env-Vars: SKIP_PYTHON_MODULES=1
 
 [catkin_pkg_modules]
+No-Python2:
 Source: catkin_pkg_modules
 Depends3: python3-dateutil, python3-docutils, python3-pyparsing, python3-packaging
 Conflicts3: catkin, python3-catkin-pkg (<< 0.3.0)