Tooltip tooltipChange subscription not cleaned up

[aeleneski]

Bug description or feature request:

In TooltipDirective there is a subscription to this.tooltipChange.subscribe that is not being unsubscribed in the ngOnDestroy method.

Plunker/StackBlitz that reproduces the issue:

Using Plunkr, StackBlitz is the best way to show your issue. Issues without link to an example of reproduction might be closed.

You can use one of starter templates:

Plunkr: https://plnkr.co/edit/0NipkZrnckZZROAcnjzB?p=preview

StackBlitz: https://stackblitz.com/edit/ngx-bootstrap?file=app%2Fapp.module.ts

Versions of ngx-bootstrap, Angular, and Bootstrap:

ngx-bootstrap: 3.2.0

Angular: 7.2.7

Bootstrap: 4.3.1

Build system: Angular CLI, System.js, webpack, starter seed: Angular CLI

[haridevelops]

#5431 closes this issue.

[haridevelops]

great if you add hacktoberfest label

[haridevelops]

Waiting for review approval