docs: fix typos

Author: pgrimaud

index.html

@@ -153,7 +153,7 @@ <h2>
         <h2>
             <a class="post-link" href="https://github.com/jyuch/gitbucket-backup-plugin"><span class="fa fa-floppy-o"></span>Backup plugin</a>
         </h2>
-        <p>Plugin providing backup functionnality for GitBucket.</p>
+        <p>Plugin providing backup functionality for GitBucket.</p>
       </li>
       <li>
          <h2>