fix build for TLS

The old way causes the following error:

root@e5028564848c:/# docker ps
FATA[0000] Get http:///var/run/docker.sock/v1.16/containers/json: dial unix /var/run/docker.sock: no such file or directory. Are you trying to connect to a TLS-enabled daemon without TLS? 

Installing via curl grabs the latest and fixes the TLS issue.