some optimization

src/users/change_password.cpp

@@ -59,7 +59,7 @@ void change_password(const httplib::Request& request, httplib::Response& respons
         return;
     }
 
-    std::ifstream usersfile("users.json");
+    std::ifstream usersfile(USERS_FILE);
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
 
@@ -114,7 +114,7 @@ void change_password(const httplib::Request& request, httplib::Response& respons
         syslog(LOG_ERR, "can't find this user in change password request");
         return;
     }
-    std::ofstream usersfilew("users.json");
+    std::ofstream usersfilew(USERS_FILE);
     usersfilew << all_users.dump(4);
     usersfilew.close();
     response.set_content(R"({"status":"ok"})", JSON_TYPE);