Switch from pathlib to pathlib2

The pathlib backport module is no longer maintained. The development
has moved to the pathlib2 module instead.

Quoting from the pathlib's README:
"Attention: this backport module isn't maintained anymore. If you want
to report issues or contribute patches, please consider the pathlib2
project instead."

tests/test_types.py

@@ -3,7 +3,10 @@
 import os
 from subprocess import PIPE
 from mock import Mock
-from pathlib import Path
+try:
+    from pathlib import Path
+except ImportError:
+    from pathlib2 import Path
 import pytest
 from tests.utils import CorrectedCommand, Rule, Command
 from thefuck import const