Add GOPROXY for go module operations
Add GOPROXY for go module operations

Without a GOPROXY, go modules are fetched from their respective hosts,
which increases the likelihood that any given host might be unavailable
and break builds.

Fixes #2036

Signed-off-by: Nolan Brubaker <e67e8ddef39e69b06b6af9ac110ddb19c04a3e39@vmware.com>

heptio/ark,heptio/ark