Install gosub with go install
[#179348306](https://www.pivotaltracker.com/story/show/179348306)
#!/bin/bash
-set -e -x
+set -exuo pipefail
# ensure gosub is installed (this will recompile it only if necessary)
-GO111MODULE=on go get github.com/vito/gosub
+go install github.com/vito/gosub@latest
FORCE_SUBMODULE_HTTPS="${FORCE_SUBMODULE_HTTPS:-false}"
rm -rf /tmp/packages
