wiki: update Ubuntu versions

[deining]

Updates Ubuntu version info given in the wiki page for Ubuntu

[gopherbot]

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/552958.
After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/552958.
After addressing review feedback, remember to publish your drafts!