Import Path from _pytest.pathlib for py35

This is important for `isinstance` checks etc.

testing/test_junitxml.py

@@ -1,7 +1,6 @@
 import os
 import platform
 from datetime import datetime
-from pathlib import Path
 from xml.dom import minidom
 
 import py
@@ -9,6 +8,7 @@ import xmlschema
 
 import pytest
 from _pytest.junitxml import LogXML
+from _pytest.pathlib import Path
 from _pytest.reports import BaseReport