Fix crash on missing feed update date

lib/frenzy/update_feeds.ex

@@ -80,11 +80,18 @@ defmodule Frenzy.UpdateFeeds do
   end
 
   defp update_feed_from_rss(feed, rss) do
+    last_updated =
+      if rss.updated_at do
+        parse_date(rss.updated_at)
+      else
+        DateTime.utc_now()
+      end
+
     changeset =
       Feed.changeset(feed, %{
         title: rss.title,
         site_url: rss.link.href,
-        last_updated: parse_date(rss.updated_at)
+        last_updated: last_updated
       })
 
     Repo.update(changeset)