Fix download timeout measurement

Using .seconds can't return more than a days worth of seconds, so
downloads stop working if you don't get them after a day of inactivity.

So, total_seconds() for the win

lutris/util/update_cache.py

@@ -42,4 +42,4 @@ def get_last_call(key):
     if not date:
         return 0
     delta = datetime.now() - date
-    return delta.seconds
+    return delta.total_seconds()