Parsing of `arrayFormat: 'comma'` not working for queries of single value with comma

Parsing of `arrayFormat: 'comma'` not working for queries of single value with comma

Say we have an Object we are stringifying to become a query param of the following shape (notice the comma in the value)

1. Create an object with its value as a single string / array of one string.

```
const singleQueryObject = { not_important: [ "I, am, one, single, value"]};

// OR (the value can also just be a plain string, not an array like the above)

const singleQueryObject = { not_important: "I, am, one, single, value" };
```

2. We stringify it:

```
const stringifyResult = queryString.stringify(singleQueryObject, { arrayFormat: 'comma' });
//=>  'not_important=I%2C%20am%2C%20one%2C%20single%2C%20value'
```

3. We parse it (Actual)

```
const parsedResult = queryString.parse(stringifyResult, { arrayFormat: 'comma' });
//=> { not_important: [ 'I', ' am', ' one', ' single', ' value' ] }
```

(Expected)
```
{ not_important: [ 'I, am, one, single, value' ] };
```

## Work around (?)
This bug only occurs when there is a **single value**. So say if we run the same step as above with this object instead:

```
const singleQueryObject = { not_important: [ 'I, am, one, single, value', 'It works!'] };
const stringifyResult = queryString.stringify(singleQueryObject, { arrayFormat: 'comma' });
const parsedResult = queryString.parse(stringifyResult, { arrayFormat: 'comma' });

//=> { not_important: [ 'I, am, one, single, value', 'It works!' ] }
```