java_stub_template different content between mirrors

Hi,

Looking [here](https://github.com/bazelbuild/rules_scala/blob/master/scala/scala.bzl#L423)

There's a difference between the sha256 digest of:
- https://raw.githubusercontent.com/bazelbuild/bazel/0.17.1/src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt (`1b93358d8d95e3fea5ad5889c8b9b0b475525986fcafb6d74725f3f21204b543`)
- https://mirror.bazel.build/raw.githubusercontent.com/bazelbuild/bazel/0.17.1/src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt (`39097bdc47407232e0fe7eed4f2c175c067b7eda95873cb76ffa76f1b4c18895`)

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How do we update either of them?

Start at scala/scala.bzl line 423 and compare the two Bazel 0.17.1 java_stub_template.txt URLs with their recorded SHA-256 values. Determine which mirror is authoritative and what update process applies; done means the referenced mirror content and digest are consistent.

Written by the indexing model from the issue text.