Update License of ydl_api as per ydl_api#6 (#2821)

README.md

@@ -184,7 +184,7 @@ _Related: [Internet of Things (IoT)](#internet-of-things-iot)_
 - [Sonarr](https://sonarr.tv/) - Automatic TV Shows downloader and manager for Usenet and BitTorrent. It can grab, sort and rename new episodes and automatically upgrade the quality of files already downloaded when a better quality format becomes available. ([Source Code](https://github.com/Sonarr/Sonarr)) `GPL-3.0` `C#`
 - [StackStorm](https://stackstorm.com) - StackStorm (aka _IFTTT for Ops_) is event-driven automation for auto-remediation, security responses, troubleshooting, deployments, and more. Includes rules engine, workflow, 160 integration packs with 6000+ actions and ChatOps. ([Source Code](https://github.com/StackStorm/st2)) `Apache-2.0` `Python`
 - [WebUI-aria2](https://github.com/ziahamza/webui-aria2) - Interface to interact with the aria2 downloader. Very simple to use, just download and open index.html in any web browser. ([Demo](https://ziahamza.github.io/webui-aria2/)) `MIT` `HTML5`
-- [ydl_api](https://github.com/Totonyus/ydl_api) - Simple youtube-dl REST API to launch downloads on a distant server. `Unlicense` `Python`
+- [ydl_api](https://github.com/Totonyus/ydl_api) - Simple youtube-dl REST API to launch downloads on a distant server. `GPL-3.0` `Python`
 - [YoutubeDL-Material](https://github.com/Tzahi12345/YoutubeDL-Material) - Material Design inspired YouTube downloader, based on youtube-dl. Supports playlists, quality select, search, dark mode and much more, all with a clean and modern design. `MIT` `Nodejs`
 - [Zenbot](https://github.com/DeviaVir/zenbot) - Zenbot is a lightweight, extendable, artificially intelligent trading bot for Bitcoin, Ether, Litecoin, and more. `MIT` `Nodejs`
 - [ZeroQueue](https://github.com/thezeroqueue/zeroqueue) - A low-code queue management system that lets you run scheduled jobs for anything. `GPL-3.0` `Nodejs`