Mark support for Ubuntu 15.10 instead of 14.10
Mark support for Ubuntu 15.10 instead of 14.10

Ubuntu 14.10 has reached end-of-life for several
months now.

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MOS_MIGRATED_REVID=107473533

davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website