javascript把json对象转为数组
转换前是这样的：
```

var articles = [{
    title: 'hello',
    content: 'hello world',
    created_at:'2017-08-30 13:45:15'
},{
    title: 'foo',
    content: 'foo bar',
    created_at:'2017-08-30 13:45:15'
}];
```
我想把它转成这样：
```
var articles2 = [
    [ 'hello', 'hello world', '2017-08-30 13:45:15' ],
    [ 'foo', 'foo bar','2017-08-30 13:46:06' ]
];
```
用js应该怎么做呢？
```
var articles = [{
    title: 'hello',
    content: 'hello world',
    created_at:'2017-08-30 13:45:15'
},{
    title: 'foo',
    content: 'foo bar',
    created_at:'2017-08-30 13:45:15'
}]
var result = articles.map(item => {
  return Object.values(item)
})
```