THIRDPARTY: Add missing license texts for CC-BY-3.0, CC-BY-SA-4.0.
THIRDPARTY: Add missing license texts for CC-BY-3.0, CC-BY-SA-4.0.

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulip.com>

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