Switch from govendor to go modules. (#587)

Thanks to @BenoitKnecht for leading the way on this.

vendor/github.com/miekg/dns/fuzz.go

@@ -0,0 +1,23 @@
+// +build fuzz
+
+package dns
+
+func Fuzz(data []byte) int {
+	msg := new(Msg)
+
+	if err := msg.Unpack(data); err != nil {
+		return 0
+	}
+	if _, err := msg.Pack(); err != nil {
+		return 0
+	}
+
+	return 1
+}
+
+func FuzzNewRR(data []byte) int {
+	if _, err := NewRR(string(data)); err != nil {
+		return 0
+	}
+	return 1
+}