The image tags for gcr.io/runconduit/go-deps and
gcr.io/runconduit/proxy-deps were not updating to account for all
changes in those images.
Modify SHA generation to include all files that affect the base
dependency images. Also add instructions to README.md for updating
hard-coded SHAs in Dockerfile's.
Fixes#115
Signed-off-by: Andrew Seigner <andrew@sig.gy>