update 1.8.0 notes (#4156)
update 1.8.0 notes (#4156)

* typos fixed
* a cache fix
* update/finalize some other bits

Signed-off-by: Miek Gieben <00b357f94cf3a1145a32703fb42e2d80418ab806@miek.nl>
chrisohaver/coredns,coredns/coredns,johnbelamaric/coredns,miekg/coredns,yongtang/coredns,miekg/coredns,johnbelamaric/coredns