Fix potential vulnerability

Author: ggeerraarrdd

templates/index.html

@@ -10,7 +10,7 @@
     <span style="color: {{ series.color3 }};">
         {{ series.series_brief.upper() }} 
         {% if series.series_poster_url %}
-        <a href="{{ series.series_poster_url }}" style="color: {{ series.color3 }};" target="_blank" target="_blank">POSTER</a>
+        <a href="{{ series.series_poster_url }}" style="color: {{ series.color3 }};" target="_blank" rel="noopener noreferrer">POSTER</a>
         {% endif %}
     </span>