net/dns: fix recently added URL scheme from http to https

I typoed/brainoed in the earlier 3582628691

Change-Id: Ic198a6f9911f195d9da9fc5259b5784a4b15e5e3
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/dns/direct_test.go

@@ -88,7 +88,7 @@ func testDirect(t *testing.T, fs wholeFileFS) {
 		t.Fatal(err)
 	}
 	want := `# resolv.conf(5) file generated by tailscale
-# For more info, see http://tailscale.com/s/resolvconf-overwrite
+# For more info, see https://tailscale.com/s/resolvconf-overwrite
 # DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN
 
 nameserver 8.8.8.8

net/dns/resolvconffile/resolvconffile.go

@@ -42,7 +42,7 @@ type Config struct {
 func (c *Config) Write(w io.Writer) error {
 	buf := new(bytes.Buffer)
 	io.WriteString(buf, "# resolv.conf(5) file generated by tailscale\n")
-	io.WriteString(buf, "# For more info, see http://tailscale.com/s/resolvconf-overwrite\n")
+	io.WriteString(buf, "# For more info, see https://tailscale.com/s/resolvconf-overwrite\n")
 	io.WriteString(buf, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
 	for _, ns := range c.Nameservers {
 		io.WriteString(buf, "nameserver ")