intercom: Dont pass undefined to string-hash

Fix uncaught error from happening when `company.name` is undefined... The hash function doesn't like it.

```
TypeError: Cannot read property 'length' of undefined
 at module.exports (node_modules/string-hash/index.js:3:17)
 at formatCompany (node_modules/segmentio-integrations/lib/intercom/index.js:227:34)
...
```

Kinda verbose... I would prefer to just do `hash(value || '')` and have it return `0`, but I am not sure how that would play with Intercom.

cc: @calvinfo @yields