minor: point to bootstrap repo main branch

index.html

@@ -410,6 +410,6 @@ <h3>Editor preferences</h3>
       <li>Set encoding to UTF-8.</li>
       <li>Add new line at end of files.</li>
     </ul>
-    <p>Consider documenting and applying these preferences to your project's <code>.editorconfig</code> file. For an example, see <a href="https://github.com/twbs/bootstrap/blob/master/.editorconfig">the one in Bootstrap</a>. Learn more <a href="https://editorconfig.org">about EditorConfig</a>.</p>
+    <p>Consider documenting and applying these preferences to your project's <code>.editorconfig</code> file. For an example, see <a href="https://github.com/twbs/bootstrap/blob/main/.editorconfig">the one in Bootstrap</a>. Learn more <a href="https://editorconfig.org">about EditorConfig</a>.</p>
   </div>
 </div>