Fix probably alive test

The probably alive funtion was fixed just prior to the Gramps 5.1.4
release. It appears the relevant unit test was not updated to match.
The relevant commit:
a685b96f70

gramps/gen/filters/rules/test/person_rules_test.py

@@ -347,7 +347,7 @@ class BaseTest(unittest.TestCase):
         """
         rule = ProbablyAlive(['1900'])
         res = self.filter_with_rule(rule)
-        self.assertEqual(len(res), 766)
+        self.assertEqual(len(res), 733)
 
     def test_RegExpName(self):
         """