use go 1.13 in go.mod which is consistent with go version used in builds
use go 1.13 in go.mod which is consistent with go version used in builds

Signed-off-by: Andrew Sy Kim <216147b618cb827f522f086e90f58ea14ddeaac5@gmail.com>

kubernetes/cloud-provider-aws,kubernetes/cloud-provider-aws,kubernetes/cloud-provider-aws