net/http: fix minor typos in Request godoc

[ivy]

Fixes missing commas where it wasn't immediately apparent whether
"requests" was being used as a verb or a noun.

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Patch Set 1:

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Message from Gerrit User 5137:

Patch Set 1: Code-Review+2

Thank you Ivy for the fixes and welcome to Go! LGTM

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This PR is being closed because golang.org/cl/135135 has been merged.