RTL not working

### Issue type
Styling

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

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

### Issue description
I have used NbThemeModule.forRoot() to change my app to Rtl but it doesn't make any changes.
**Current behavior:**
nothing happened

**Expected behavior:**
change the dir attribute in tag its fixed to ltr

**Steps to reproduce:**

**Related code:**

```
insert short code snippets here
export class ThemeModule {
static forRoot(): ModuleWithProviders {
return {
ngModule: ThemeModule,
providers: [
...NbThemeModule.forRoot(
{
name: 'default',
},
[DEFAULT_THEME, COSMIC_THEME, CORPORATE_THEME, DARK_THEME],
null,
NbLayoutDirection.RTL
).providers,
],
};
}
}
```

### Other information:

**npm, node, OS, Browser**
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```

**Angular, Nebular**
```

```