Update config.yml to fix the Discord url

Author: mrkara

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,5 @@
 blank_issues_enabled: false
 contact_links:
   - name: ❓ Ask a question or discuss an idea
-    url: https://discord.gg/casperblockchain
+    url: https://discord.gg/caspernetwork
     about: Ask your questions and discuss your ideas in the `#smart-contracts` channel