Use https to open pxt-sample (#5524)
Use https to open pxt-sample (#5524)

pxt-sample uses [`window.applicationCache`](https://developer.mozilla.org/en-US/docs/Web/API/Window/applicationCache). On chrome window.applicationCache is null when using non-secure url. This prevents the website from loading
switch-education/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,Microsoft/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,switch-education/pxt