Docs: Fix Typo in license version

- Typo in Apache License version for ESP_MQTT

Merges https://github.com/espressif/esp-idf/issues/7311

docs/en/COPYRIGHT.rst

@@ -57,7 +57,7 @@ These third party libraries can be included into the application (firmware) prod
 
 * :component:`Asio <asio>`, Copyright (c) 2003-2018 Christopher M. Kohlhoff is licensed under the Boost Software License as described in :component_file:`COPYING file<asio/asio/asio/COPYING>`.
 
-* :component:`ESP-MQTT <mqtt>` MQTT Package (contiki-mqtt) - Copyright (c) 2014, Stephen Robinson, MQTT-ESP - Tuan PM <tuanpm at live dot com> is licensed under Apache License 2,0 as described in :component_file:`LICENSE file <mqtt/esp-mqtt/LICENSE>`.
+* :component:`ESP-MQTT <mqtt>` MQTT Package (contiki-mqtt) - Copyright (c) 2014, Stephen Robinson, MQTT-ESP - Tuan PM <tuanpm at live dot com> is licensed under Apache License 2.0 as described in :component_file:`LICENSE file <mqtt/esp-mqtt/LICENSE>`.
 
 * :component:`BLE Mesh <bt/esp_ble_mesh>` is adapted from Zephyr Project, Copyright (c) 2017-2018 Intel Corporation and licensed under Apache License 2.0