Fixed confluence add_user_group to use right URL (#1425)

* Fixed add_user_group to use right URL

* Fixed indentation

atlassian/confluence.py

@@ -3068,10 +3068,8 @@ def add_user_to_group(self, username, group_name):
         :param group_name: str - name of group to add user to
         :return: Current state of the group
         """
-        url = "rest/api/2/group/user"
-        params = {"groupname": group_name}
-        data = {"name": username}
-        return self.post(url, params=params, data=data)
+        url = f"rest/api/user/{username}/group/{group_name}"
+        return self.put(url)
 
     def add_space_permissions(
         self,