devel: fix grammar mistake a HTTP => an HTTP

Closes: #546

Author: jelly

templates/devel/tier0_mirror.html

@@ -7,7 +7,7 @@
 <div class="box">
 
     <h2>Tier 0 Mirror usage information</h2>
-    <p>Arch Linux Tier 0 mirror on <a href="https://repos.archlinux.org">repos.archlinux.org</a> which can be used if to obtain the absolute latest packages. The mirror is protected with a HTTP Basic Auth password unique per Staff member.</p>
+    <p>Arch Linux Tier 0 mirror on <a href="https://repos.archlinux.org">repos.archlinux.org</a> which can be used if to obtain the absolute latest packages. The mirror is protected with an HTTP Basic Auth password unique per Staff member.</p>
     {% if mirror_url %}
       <code id="serverinfo">Server = {{ mirror_url }}</code> <button id="copybutton">Copy to clipboard</button>