[release-branch.go1.12] go1.12.13

Change-Id: Ic4db4625c4b7031aa08cb235f526267058a50430
Reviewed-on: https://go-review.googlesource.com/c/go/+/204641
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>

VERSION

-go1.12.12
+go1.12.13
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