Update google.go
Update google.go

Make "cd" check case-insensitive.

--- a/doh-server/google.go
+++ b/doh-server/google.go
@@ -71,9 +71,9 @@
 
 	cdStr := r.FormValue("cd")
 	cd := false
-	if cdStr == "1" || strings.ToUpper(cdStr) == "TRUE" {
+	if cdStr == "1" || strings.EqualFold(cdStr, "true") {
 		cd = true
-	} else if cdStr == "0" || strings.ToUpper(cdStr) == "FALSE" || cdStr == "" {
+	} else if cdStr == "0" || strings.EqualFold(cdStr, "false") || cdStr == "" {
 	} else {
 		return &DNSRequest{
 			errcode: 400,