feat: fix integer priority sorting (apache#327)

* fix: fix integer priority sorting

* fix: fix formatting with black

Author: nschwane

casbin/model/model.py

@@ -124,7 +124,12 @@ def sort_policies_by_priority(self):
             if assertion.priority_index == -1:
                 continue
 
-            assertion.policy = sorted(assertion.policy, key=lambda x: x[assertion.priority_index])
+            assertion.policy = sorted(
+                assertion.policy,
+                key=lambda x: int(x[assertion.priority_index])
+                if x[assertion.priority_index].isdigit()
+                else x[assertion.priority_index],
+            )
 
             for i, policy in enumerate(assertion.policy):
                 assertion.policy_map[",".join(policy)] = i