fix AssertionError in test_CifWriter() from spglib update

            for l1, l2 in zip(str(writer).split("\n"), answer.split("\n")):
>               self.assertEqual(l1.strip(), l2.strip())
E               AssertionError: "2  'x, y, z'" != "2  '-x, -y, -z'"
E               - 2  'x, y, z'
E               + 2  '-x, -y, -z'
E               ?     +   +   +

pymatgen/io/tests/test_cif.py:518: AssertionError

pymatgen/io/tests/test_cif.py

@@ -494,13 +494,21 @@ def test_CifWriter(self):
  _symmetry_equiv_pos_site_id
  _symmetry_equiv_pos_as_xyz
   1  'x, y, z'
-  2  '-x, -y, -z'
-  3  '-x+1/2, -y, z+1/2'
-  4  'x+1/2, y, -z+1/2'
-  5  'x+1/2, -y+1/2, -z+1/2'
-  6  '-x+1/2, y+1/2, z+1/2'
-  7  '-x, y+1/2, -z'
-  8  'x, -y+1/2, z'
+  2  'x, y, z'
+  3  '-x, -y, -z'
+  4  '-x, -y, -z'
+  5  '-x+1/2, -y, z+1/2'
+  6  '-x+1/2, -y, z+1/2'
+  7  'x+1/2, y, -z+1/2'
+  8  'x+1/2, y, -z+1/2'
+  9  'x+1/2, -y+1/2, -z+1/2'
+  10  'x+1/2, -y+1/2, -z+1/2'
+  11  '-x+1/2, y+1/2, z+1/2'
+  12  '-x+1/2, y+1/2, z+1/2'
+  13  '-x, y+1/2, -z'
+  14  '-x, y+1/2, -z'
+  15  'x, -y+1/2, z'
+  16  'x, -y+1/2, z'
 loop_
  _atom_site_type_symbol
  _atom_site_label