Update kokoro bazel version to 0.6.0
Update kokoro bazel version to 0.6.0

Also updated closure rules version to be compatible with bazel 0.6.0.

See: https://github.com/bazelbuild/rules_closure/releases/tag/0.4.2

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171222636

google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus