NbSelect is empty on init (uses translate pipe from ngx-translate)

### NbSelect initial value not selected

**I'm submitting a ...** (check one with "x")

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**

We use Nebular on our project. It's awesome. Keep up the good work.

However, we use NbSelect for the language options. On initial selected value ('en'), NbSelect is empty and kind of shrinked. Language options are array of strings (['en', 'es', ...]). If select is clicked and no option choosed, it is fixed. As far I can tell, translate pipe is causing the issue here. (nxg-translate)

**Expected behavior:**

Initial value to be selected.

**Steps to reproduce:**

**Related code:**

```

{{
'languages.' + language | translate
}}

```

### Other information:

**npm, node, OS, Browser**
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**Angular, Nebular**
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