Fix test_backtrack.py (#865)

Fix invalid test related to t.sort() vs sorted(t)

Author: Brknyi

tests/test_backtrack.py

@@ -184,8 +184,9 @@ def test_normal(self):
         ]
 
         words = ["oath", "pea", "eat", "rain"]
-        self.assertEqual(find_words(board, words).sort(),
-                         ['oath', 'eat'].sort())
+        result = find_words(board, words)
+        test_result = ['oath', 'eat']
+        self.assertEqual(sorted(result),sorted(test_result))
 
     def test_none(self):
         board = [