Fix doc on "Multiple outputs" for runtime_deps.

Review-Url: https://codereview.chromium.org/2033443002
Cr-Original-Commit-Position: refs/heads/master@{#397309}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0e85587e05893b1a8b53d8c80f38506dd3b06713