Update EasyList filter rules URL for ad blocker

The previously used URL is a redirect, and the new URL in this patch is
a direct link, which is also the URL given at the AdBlockPlus subscriptions
page (https://adblockplus.org/en/subscriptions). Using a direct URL loads
rules marginally faster, and seems to behave more robustly for fetching
updated rule sets.

This fixes https://bugzilla.gnome.org/show_bug.cgi?id=710661