fix error formatting (#3639)
fix error formatting (#3639)

Signed-off-by: Chris O'Haver <c8d69f6e0f4a592980d82af78b0efddff3dcc387@infoblox.com>
chrisohaver/coredns,johnbelamaric/coredns,coredns/coredns,yongtang/coredns,johnbelamaric/coredns,miekg/coredns,miekg/coredns