fix: make dependency source use superscript tag

Avoid using special characters and use '<sup>' HTML tag instead.
To not rely on user's fonts Unicode coverage.

Closes: #490
Signed-off-by: Hanabishi <1722-hanabishi@users.noreply.gitlab.archlinux.org>

templates/partials/packages/package_metadata.html

@@ -21,7 +21,7 @@
                 {% else -%}
                     </a>
                     {%- if dep.is_aur_package() -%}
-                        ᴬᵁᴿ
+                        <sup><small>AUR</small></sup>
                     {% endif %}
                 {% endif %}