Update release note for 1.8.7 (#5007)

This PR updates release notes for 1.8.7 to prepare for issue 4996.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

notes/coredns-1.8.7.md

++++
+title = "CoreDNS-1.8.7 Release"
+description = "CoreDNS-1.8.7 Release Notes."
+tags = ["Release", "1.8.7", "Notes"]
+release = "1.8.7"
+date = "2021-11-25T00:00:00+00:00"
+author = "coredns"
++++
+
+This is a release with bug fixes and some new features added. We now enable HTTP/2 in
+gRPC service (https://github.com/coredns/coredns/pull/4842). The shuffling algorithm
+in loadbalance plugin has also been improved to have a more consistent
+behavior (https://github.com/coredns/coredns/pull/4961).
+
+## Brought to You By
+
+Chris O'Haver,
+Christian Ang,
+Cyb3r Jak3,
+Denis Tingaikin,
+gomakesix,
+Hu Shuai,
+Humberto Leal,
+Johnny Bergström,
+Matt Palmer,
+Miek Gieben,
+OctoHuman,
+Ondřej Benkovský,
+Pavol Lieskovský,
+Vector,
+Wu Shuang,
+xuweiwei,
+xww,
+Yong Tang,
+ZhangJian He,
+Zou Nengren
+
+## Noteworthy Changes
+
+* core: Support plain HTTP for DoH (https://github.com/coredns/coredns/pull/4997)
+* plugin/auto: Fix panic caused by config invalid reload value (https://github.com/coredns/coredns/pull/4986)
+* plugin/cache: fix data race (https://github.com/coredns/coredns/pull/4932)
+* plugin/file: Fix print tree error (https://github.com/coredns/coredns/pull/4962)
+* plugin/forward: Use new msg.Id for upstream queries (https://github.com/coredns/coredns/pull/4841)
+* plugin/grpc: Enable HTTP/2 in gRPC service (https://github.com/coredns/coredns/pull/4842)
+* plugin/k8s_external: Fix SRV queries doesn't work with AWS ELB/NLB (https://github.com/coredns/coredns/pull/4929)
+* plugin/loadbalance: More consistent shuffling (https://github.com/coredns/coredns/pull/4961)
+* plugin/metrics: Support HTTPS qType in requests count metric label (https://github.com/coredns/coredns/pull/4934)
+* plugin/metrics: Expand coredns_dns_responses_total with plugin label (https://github.com/coredns/coredns/pull/4914)
+* plugin/route53: Configurable AWS Endpoint (https://github.com/coredns/coredns/pull/4963)