Bug with russian locale and nb-rangepicker component

### Issue type

* [x] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**
When add russian locale, nb-rangepicker component doesn't show selected result in input control.

**Expected behavior:**
Input control must have a value after range selection

**Steps to reproduce:**
1. Add russian locale (in app.module.ts)
2. Go to '/pages/forms/datepicker', component 'Datepicker With Range'

**Related code:**

```
// app.module.ts
...
import { NgModule, LOCALE_ID } from '@angular/core';
import { registerLocaleData } from '@angular/common';
import localeRu from '@angular/common/locales/ru';
registerLocaleData(localeRu, 'ru');
...

@NgModule({
...
providers: [
...
{ provide: LOCALE_ID, useValue: 'ru' }
],
bootstrap: [AppComponent]
})
```