[release-branch.go1.12] go1.12.4

Change-Id: I4d1b5e00ab4480b4c5adeeb4f53ddfdfa3903b71
Reviewed-on: https://go-review.googlesource.com/c/go/+/171838
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

VERSION

-go1.12.3
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+go1.12.4
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