Fix Discord server link in contributing guide (#71)

Updated Discord invite link in CONTRIBUTING.md

Signed-off-by: fredbi <fredbi@yahoo.com>

Author: fredbi

docs/doc-site/project/contributing/CONTRIBUTING.md

@@ -53,7 +53,7 @@ You may also join our discord server where you may discuss issues or requests.
 [![Discord Server][discord-badge]][discord-url]
 
 [discord-badge]: https://img.shields.io/discord/1446918742398341256?logo=discord&label=discord&color=blue
-[discord-url]: https://discord.gg/DrafRmZx
+[discord-url]: https://discord.gg/twZ9BwT3
 {{% /tab %}}
 
 {{% tab title="Reporting issues" %}}