build: update download URL for Boost
build: update download URL for Boost

boost project does not host its dist tarballs at bintray anymore.
let's use the new place. and take this opportunity to use the
latest boost stable release at the time of writing.

Signed-off-by: Kefu Chai <cdc92d111bae0ed1ee3b3c8a1f849fcffc6b44f7@gmail.com>
Message-Id: <20211004001535.26104-1-cdc92d111bae0ed1ee3b3c8a1f849fcffc6b44f7@gmail.com>

scylladb/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar