Update new forum URL (#519)

Author: st-Wook

.github/ISSUE_TEMPLATE/config.yml

@@ -4,5 +4,5 @@ contact_links:
     url: https://discord.gg/rjdYHvj
     about: Discuss on the forum or on the Discord to get help with an example or create a new one.
   - name: GDevelop Forums
-    url: https://forum.gdevelop-app.com
+    url: https://forum.gdevelop.io
     about: You can also discuss examples on the forum.