Make remaining curl respect HOMEBREW_CURLRC

[lembacon]

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Make the curl invocation in cmd/update and utils/analytics both respect the HOMEBREW_CURLRC environment variable, as utils/curl already does so, otherwise the annoying warning Failed to set filetime on outfile: Operation not permitted will pop up every time brew update running.

[MikeMcQuaid]

Looks good, thanks @lembacon! Merge when ready.