发出解析Yaml文件的问题

I have the following struct which filled after parsing yaml file The issue is that the quote is missing

File in.yaml

e.g.

_schema: "3.0.0"
bar:
- one

File out.yaml

_schema: 3.0.0
bar:
- one

As you can see I got 3.0.0 instead the “3.0.0” , Any idea how to overcome this

This is a small program which I've created to demonstrate the issue

package main

import (
    "gopkg.in/yaml.v2"
    "io/ioutil"
)

type Config struct {
    Schema string `yaml:"_schema"`
    Bar []string
}

func main() {

    cfg := Config{}
    source, err := ioutil.ReadFile("in.yaml")
    if err != nil {
        panic(err)
    }
    err = yaml.Unmarshal([]byte(source), &cfg)
    if err != nil {
        panic(err)
    }
    y, _ := yaml.Marshal(&cfg)
    err = ioutil.WriteFile("out.yaml", y, 0644)}

}