use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/xenolf/lego/challenge/dns01/cname.go

@@ -0,0 +1,16 @@
+package dns01 // import "github.com/xenolf/lego/challenge/dns01"
+
+import "github.com/miekg/dns"
+
+// Update FQDN with CNAME if any
+func updateDomainWithCName(r *dns.Msg, fqdn string) string {
+	for _, rr := range r.Answer {
+		if cn, ok := rr.(*dns.CNAME); ok {
+			if cn.Hdr.Name == fqdn {
+				return cn.Target
+			}
+		}
+	}
+
+	return fqdn
+}