Fix pytest_collect_file sig

pytest_doctestplus/plugin.py

@@ -588,7 +588,7 @@ def get_list_opt(name):
             # Let other plugins decide the outcome.
             return None
 
-        def pytest_collect_file(self, collection_path, parent):
+        def pytest_collect_file(self, file_path, parent):
             """Implements an enhanced version of the doctest module from py.test
             (specifically, as enabled by the --doctest-modules option) which
             supports skipping all doctests in a specific docstring by way of a