Provide automatic removal of pkg-resources==0.0.0

Should help to deal with that pretty paintuly issue under Ubuntu/Debian
family:
https://bugs.launchpad.net/ubuntu/+source/python-pip/+bug/1635463
diff --git a/tests/requirements_txt_fixer_test.py b/tests/requirements_txt_fixer_test.py
index 87e7b0c..437cebd 100644
--- a/tests/requirements_txt_fixer_test.py
+++ b/tests/requirements_txt_fixer_test.py
@@ -28,6 +28,8 @@
             FAIL,
             b'Django\n-e git+ssh://git_url@tag#egg=ocflib\nPyMySQL\n',
         ),
+        (b'bar\npkg-resources==0.0.0\nfoo\n', FAIL, b'bar\nfoo\n'),
+        (b'foo\npkg-resources==0.0.0\nbar\n', FAIL, b'bar\nfoo\n'),
     ),
 )
 def test_integration(input_s, expected_retval, output, tmpdir):