Amazon has changed the domain that they use to serve Fire TV software updates
Amazon has switched from using the domain amzdigital-a.akamaihd.net to now using the domain d1s31zyz7dcc2d.cloudfront.net for serving software update files to Fire TV devices. This is only important to know if you are someone who is currently blocking Fire TV software updates by denying access to Amazon’s file hosting domain. If you have router or DNS filters set, you should update them to include the domain d1s31zyz7dcc2d.cloudfront.net. It is unknown if the sub-domain d1s31zyz7dcc2d is fixed or if it will change with each release, but all 126.96.36.199 software update files arrived on my Fire TVs and Fire TV Sticks from that same exact sub-domain.
10/30/18 Software update 188.8.131.52 is being served by the same exact subdomain (d1s31zyz7dcc2d) so, for the time being, it appears as though it will not change from update to update.