[WEB-632] Jar files not downloadable over IPv6

In order to begin a Minecraft instance, the launcher needs to be able download the jar files. Single stack IPv6 hosts cannot download those files from AWS since s3.amazonaws.com is not reachable over IPv6. However Amazon now supports IPv6 on S3 instances, since August 2016 (see blog post at https://aws.amazon.com/blogs/aws/now-available-ipv6-support-for-amazon-s3/), but the customer has to switch an IPv6 enabled endpoint like https://BUCKET.s3.dualstack.REGION.amazonaws.com or https://s3.dualstack.REGION.amazonaws.com/BUCKET