Update Discord link

Original link used on website has expired. Replaced it with a permanent link.

content/template_main.html

@@ -20,7 +20,7 @@ <h2>Safe <a href="https://www.rust-lang.org/">Rust</a> wrapper around
  <li><a href="/"><i class="fas fa-globe"></i> Home</a></li>
  <li><a href="/guide/introduction"><i class="fas fa-book"></i> Guide</a></li>
  <li><a href="https://docs.rs/vulkano"><i class="fab fa-rust"></i> API</a></li>
- <li><a href="https://discord.gg/GrEqcbk4"><i class="fab fa-discord"></i> Discord</a></li>
+ <li><a href="https://discord.gg/bncB9W2VDV"><i class="fab fa-discord"></i> Discord</a></li>
  <li><a href="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/vulkano-rs/vulkano"><i class="fas fa-hands-helping"></i> Contribute</a></li>
  <li><a href="/donate"><i class="fas fa-hand-spock"></i> Donate</a></li>
  </ul>