Calendars Bug

### Issue type

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

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

### Issue description
Bug in datepickers

**Current behavior:**
In all the datepickers (common and range), when i open the datepicker it shows March month instead of February and when I'm on Jan and swipe right to Feb it goes straight to Mar, and when I swipe back left it then shows Feb.

**Expected behavior:**
Show Feb when opening datepicker on month mode or when swiping right from Jan it should move to Feb and not to Mar

**Steps to reproduce:**
Open ngx-admin-demo, in Forms > Datepicker > Common Datepicker > Swipe from Jan to the right > Mar will be shown instead of Feb

**Related code:**
ngx-admin-demo : nb-datepicker / nb-rangepicker

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### Other information:

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

Node, npm: node v11.5.0 and npm v6.5.0
OS: Windows 7
Browser: Chrome

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**Angular, Nebular**
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Thank you.