Bump version to 1.6.7 (#3594)
Bump version to 1.6.7 (#3594)

Signed-off-by: Dominic Yin <d8342e5214b8c7e83a2e05beba08ad7fd40ceac7@inspur.com>
coredns/coredns,miekg/coredns,yongtang/coredns,johnbelamaric/coredns,miekg/coredns,chrisohaver/coredns,johnbelamaric/coredns