Allow the component to be destroyed

This fix the javascript errors, ObjectUnsubscribedError,
that were thrown when navigating away from a page with
the progress bar to a page without the progress bar.

Fixes MurhafSousli#27
Fixes MurhafSousli#28
Fixes MurhafSousli#33
Fixes MurhafSousli#41
Fixes MurhafSousli#81
Fixes MurhafSousli#82

README.md

@@ -59,7 +59,7 @@ import { NgProgressModule } from 'ngx-progressbar';
 })
 ```
 
-In your root component **(or any component that does not get destroyed)!**
+In your template
 
 ```html
 <ng-progress></ng-progress>

src/components/progress.component.ts

@@ -1,5 +1,5 @@
 import {
-  Component, Input, ChangeDetectionStrategy, OnChanges, SimpleChanges, OnDestroy
+  Component, Input, ChangeDetectionStrategy, OnChanges, SimpleChanges
 } from '@angular/core';
 import { NgProgressService } from '../services/progress.service';
 
@@ -25,7 +25,7 @@ import { NgProgressService } from '../services/progress.service';
   changeDetection: ChangeDetectionStrategy.OnPush
 })
 
-export class ProgressComponent implements OnChanges, OnDestroy {
+export class ProgressComponent implements OnChanges {
 
   /** Progress options  */
   @Input() ease = 'linear';
@@ -95,9 +95,4 @@ export class ProgressComponent implements OnChanges, OnDestroy {
     }
   }
 
-  ngOnDestroy() {
-    this.progress.state.unsubscribe();
-    this.progress.trickling.unsubscribe();
-  }
-
 }