Previously, commit 102616b158 tried to
expose GOPROXY env var from developer environment by specifying it as
environment variable or build argument to container build process. But
using --build-arg to container build command would require the same to
be referenced inside Dockerfile/Containerfile so that the following
warning can be avoided:
[Warning] one or more build args were not consumed: [GOPROXY]
Signed-off-by: Anoop C S <anoopcs@cryptolab.net>