fix: fix hashmap thread unsafe (casbin#299)

Signed-off-by: imp2002 <[email protected]>

Signed-off-by: imp2002 <[email protected]>

Author: imp2002

src/main/java/org/casbin/jcasbin/util/BuiltInFunctions.java

@@ -345,7 +345,7 @@ public static class GenerateGFunctionClass {
          * @return the function.
          */
         public static AviatorFunction generateGFunction(String name, RoleManager rm) {
-            memorizedMap.put(name, new HashMap<>());
+            memorizedMap.put(name, new ConcurrentHashMap<>());
 
             return new AbstractVariadicFunction() {
                 @Override