title: How to downgrade the dependencies for npm packages in StackBlitz?
body: <p>I'm trying to create an app for demo propose on StackBlitz and must use Angular 5.2.x because my app is still using 5.2.x. I just can't downgrade from v6 to v5.2 when I try to install the dependencies.</p>
  
  <p>I actually need e.g. <code>"@angular/common": "^5.2.10", "rxjs": "^5.5.10", "@angular/http": "^5.2.10"</code> etc. But it just force me to install the v6.</p>
  
  <p>Is there a possibilities to avoid this and install the needed versions or there is no way?</p>
  
  <p>Have been checking the doc for Stackblitz, but didn't find something talking about such case.</p>