Tabs content not displayed until click

### Issue type

**I'm submitting a ...**

* [X] bug report
* [ ] feature request

### Issue description

**Current behavior:**
When a `@handsontable/angular"` element inside tabs, content is not displayed until a click event inside the tab.

**Expected behavior:**
The content should appear as soon as loaded.

**Steps to reproduce:**
In any Nebular view, add a tabs component with an handsome table element. Notice that no content is displayed, and when clicking in the white area where data should be displayed, then the tab content is displayed.

**Related code:**
I've been trying to add an example on StackBlitz but I keep getting an error while importing the default theme:

Import error, can't find file:
/~@nebular/theme/styles/prebuilt/default.scss

see [https://stackblitz.com/edit/angular-nebular-integration](https://stackblitz.com/edit/angular-nebular-integration)

```
insert short code snippets here
```

// Data source
const sheetData = [['first','second'], ['1', '2'], ['3', '4'], ['5', '6']];

### Other information:

**npm, node, OS, Browser**
Chrome 70.0.3538.102 for Mac.

**Angular, Nebular**

"@angular-redux/store": "^9.0.0",
"@angular/animations": "^7.0.4",
"@angular/cdk": "^7.0.4",
"@angular/common": "^7.0.4",
"@angular/compiler": "^7.0.4",
"@angular/core": "^7.0.4",
"@angular/flex-layout": "^7.0.0-beta.19",
"@angular/forms": "^7.0.4",
"@angular/http": "^7.0.4",
"@angular/platform-browser": "^7.0.4",
"@angular/platform-browser-dynamic": "^7.0.4",
"@angular/router": "^7.0.4",
"@angular/service-worker": "^7.0.4",
"@fortawesome/fontawesome-free": "^5.5.0",
"@handsontable/angular": "^2.0.0",
"@nebular/bootstrap": "^3.0.0",
"@nebular/theme": "^3.0.0",