docs: Updated version history with 1.13.8 release notes.#14742

Merged

mattklein123 merged 2 commits intoenvoyproxy:mainfrom

cpakulski:close_rel1.13

Jan 19, 2021

Commits on Jan 18, 2021

Closing release 1.13.8
cpakulski
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Commits on Jan 19, 2021

Corrected format in release notes.
cpakulski
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