Use simpler assert in basic example.

Doc/library/unittest.rst

diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index f41bab3..10e415b 100644
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -127,13 +127,13 @@
 
        def test_choice(self):
            element = random.choice(self.seq)
-           self.assertIn(element, self.seq)
+           self.assertTrue(element in self.seq)
 
        def test_sample(self):
            with self.assertRaises(ValueError):
                random.sample(self.seq, 20)
            for element in random.sample(self.seq, 5):
-               self.assertIn(element, self.seq)
+               self.assertTrue(element in self.seq)
 
    if __name__ == '__main__':
        unittest.main()