nb-datepicker issue with NbDateFnsDateModule

### Issue type

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

* [X] bug report
* [ ] feature request

### Issue description

**Current behavior:**
After installing `@nebular/date-fns` and importing `NbDateFnsDateModule` from `app.module.ts` I still get this error printed in the console:

> ERROR Error: Can't format native date. To use custom formatting you have to install @nebular/moment or @nebular/date-fns package and import NbMomentDateModule or NbDateFnsDateModule accordingly.More information at "Formatting issue" https://akveo.github.io/nebular/docs/components/datepicker/overview#nbdatepickercomponent

**Expected behavior:**
I don't know if the component is parsing correctly the date, but when I select a date I can see it displayed correctly in the format I've set.

**Related code:**
My nb-datepicker code:

```

PLEASE NOTE: this might be related to #1088 (now closed) but it is still there.

EDIT: I've also noticed that the format is wrong: If I choose "April 8, 2019" (today) I get "2019-04-08" in the input field, but fetching from TS I get: ""2019-04-07T22:00:00.000Z" that is 1 day backward and contains "T22:00:00.000Z" that cause problem server-side.