Multi-Select does not work

[faizan-ali]

[x ] bug report
[ ] feature request
[ ] support request

**Current behavior**
The library refreshes the currently selected array of items every time upon selection. Simply put, the array is erased and the newly selected item is added. Only a single row is highlighted at any time.

**Expected behavior**
The array bound to the [selected] input should be added to, not erased upon selecting a new item. Multiple rows should be highlighted

**Reproduction of the problem**
Tried the demo code:
https://github.com/swimlane/ngx-datatable/blob/master/demo/selection/selection-multi.ts
Does not work for checkboxes either:
https://github.com/swimlane/ngx-datatable/blob/master/demo/selection/selection-chkbox.ts

**Please tell us about your environment:**
Windows 10

* **Table version:** 0.7.x
"@swimlane/ngx-datatable": "^4.0.0"

* **Angular version:** 2.0.x
Angular 2.0.0 with CLI

* **Browser:** [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
Chrome, Edge, Firefox

* **Language:** [all | TypeScript X.X | ES6/7 | ES5]
TypeScript 2.0.10

Please let me know if I have misunderstood the documentation/demo code

[amcdnl]

Fixed in 4.1.0