Allow unicode type in given step names in Py 2

Allows the given step name to be unicode in Py2. 

Py 3 is not affected. It still does not allow non-ascii characters as they're not allowed in Py 2 `__name__`s.

Author: blaise-io

pytest_bdd/steps.py

@@ -85,7 +85,7 @@ def step_func(request):
 
         step_func.step_type = GIVEN
         step_func.converters = converters
-        step_func.__name__ = name
+        step_func.__name__ = force_encode(name, 'ascii')
         step_func.fixture = fixture
         func = pytest.fixture(scope=scope)(lambda: step_func)
         func.__doc__ = 'Alias for the "{0}" fixture.'.format(fixture)