env/netbsd-amd64: update to NetBSD 8.1

NetBSD 8.1 is a bugfix release on the stable (8) branch and has
a number of recommended updates and fixes.

Updates golang/go#31858

Change-Id: Id0f4a2180af1f84486aa6bc1c4406c5e8d5a0cb3
Reviewed-on: https://go-review.googlesource.com/c/build/+/185217
Reviewed-by: Andrew Bonventre <[email protected]>

Author: bsiegert

env/netbsd-amd64/make.bash

@@ -16,7 +16,7 @@ set -e -x
 ANITA_VERSION=1.44
 ARCH=amd64
 # The release that the packages have been built for.
-RELEASE=8.0_2018Q1
+RELEASE=8.0_2019Q1
 
 # Must use GNU tar. On NetBSD, tar is BSD tar and gtar is GNU.
 TAR=tar

env/netbsd-amd64/mkvm.py

@@ -82,7 +82,7 @@ def find_latest_release(branch, arch):
 
 
 a = anita.Anita(
-    anita.URL('https://cdn.netbsd.org/pub/NetBSD/NetBSD-8.0_RC1/%s/' % arch),
+    anita.URL('https://cdn.netbsd.org/pub/NetBSD/NetBSD-8.1/%s/' % arch),
     workdir="work-NetBSD-%s" % arch,
     disk_size="4G",
     memory_size = "1G",