Add isISO6392() method 

Since there was a featured that was requested for addition of 
```javascript 
isISO6391()
```
I also feel that we can add 
```javascript
isISO6292()
```

Reference: https://en.wikipedia.org/wiki/ISO_639-2

For more `ISO 693` you can refer to https://en.wikipedia.org/wiki/ISO_639

Cc. @profnandaa, let us have your view on this feature and other ISO 639 features. 
