Fix Python 3.8 support

.travis.yml

@@ -5,6 +5,7 @@ python:
   - "3.5"
   - "3.6"
   - "3.7"
+  - "3.8-dev"
 
 install: pip install tox tox-travis
 

pytest_bdd/steps.py

@@ -220,6 +220,8 @@ def recreate_function(func, module=None, name=None, add_args=[], firstlineno=Non
     ]
     if six.PY3:
         argnames.insert(1, "co_kwonlyargcount")
+        if sys.version_info.minor >= 8:
+            argnames.insert(1, "co_posonlyargcount")
 
     for arg in get_args(func):
         if arg in add_args:

tox.ini

@@ -3,7 +3,7 @@ distshare = {homedir}/.tox/distshare
 envlist = py27-pytestlatest-linters,
           py27-pytest{36,37,38,39,310,4,41,42,43,44,45,46},
           py37-pytest{36,37,38,39,310,4,41,42,43,44,45,46,5,latest},
-          py{35,36}-pytestlatest,
+          py{35,36,38}-pytestlatest,
           py27-pytestlatest-xdist
 skip_missing_interpreters = true