更新read me

funtion.go

@@ -35,7 +35,7 @@ var adatperMapper = map[Adapter]func(l *Logger, level Level) error{
 	AdapterElasticSearch: func(l *Logger, level Level) error {
 
 		dsn := "http://es-cn-0pp1mm3hq000dnbh4.public.elasticsearch.aliyuncs.com:9200/"
-		if envkey == "prod" || envkey == "" || envkey == "gray" {
+		if os.Getenv(envkey) == "prod" || os.Getenv(envkey) == "" || os.Getenv(envkey) == "gray" {
 			dsn = "http://es-cn-0pp1mm3hq000dnbh4.elasticsearch.aliyuncs.com:9200/"
 		}