https redirect: use location.replace(...) instead of location.href = ...

Currently, when redirecting from http to https, there will be
to history entries in the browser.
Pressing "back" will go back to "http", and YoutubeCente, in turn,
will redirect to "https" again, effectively causing an infinite loop.

use location.replace() instead, because that does not create another
history entry in the browser and the back button works as expected.