Add Google mirror URL for bazel-skylib (#396)
Add Google mirror URL for bazel-skylib (#396)

Add a storage.googleapis.com/bazel-mirror URL for bazel-skylib,
so as not to hammer github (and get rate-limited).
bazelbuild/rules_webtesting,bazelbuild/rules_webtesting,bazelbuild/rules_webtesting,bazelbuild/rules_webtesting