How to properly detect domains?

How would one use Joi to validate social media URLs?

I tried this but had no luck:
```
const devSchema = Joi.object().keys({
  instagram: Joi.string().uri({
    scheme: "instagram"
  })
});
```
When I try `{instagram: "http://instagram.com/user"}`:

```
"instagram" must be a valid uri with a scheme matching the instagram pattern
```