fix(extraction): update bazel-extractor Docker image to clang-6.0 (#4066)
fix(extraction): update bazel-extractor Docker image to clang-6.0 (#4066)

This version of clang supports the cc_configure change made in https://github.com/bazelbuild/bazel/commit/cdd0c3cdba270115940e8ca5ec8104cbcd694671#diff-9899f9deb6047fe5ab4a4d2f8a96122e.
kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe