Calendar weeknumber is wrong for locale 'DE'

### Issue type

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

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
Weeknumber is wrong for locale DE. Year starts at weeknumber 2

**Expected behavior:**
Should start with 1

**Related code:**

https://stackblitz.com/edit/github-mbtqwv-r2cv5a

### Other information:

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

```

**Angular, Nebular**
```

```