Update numerous toolchain components.
Update numerous toolchain components.

These changes fix a build error currently at HEAD and are also needed to
prepare for building gke-exec-auth-plugin for Windows.

Updates:
  - go toolchain to 1.13
  - rules_go to v0.20.0
  - gazelle to v0.19.0
  - rules_docker to v0.11.0

io_bazel_rules_go needs updating for
https://github.com/bazelbuild/rules_go/pull/2118
(https://github.com/bazelbuild/rules_go/issues/1240).

bazel_gazelle and go_sdk need updating for compatibility with updated
vendor/ targets.

rules_docker needs updating to eliminate failures when running `bazel
build ...` at HEAD. The corresponding update to the go toolchain is
needed to completely eliminate the failures. For some more details see:
https://gist.github.com/pjh/3e409e8d73dad63782b333c6535696de

kubernetes/cloud-provider-gcp,kubernetes/cloud-provider-gcp