added support for "open" follow https:// links

Hi,

Was using rainbowstream for a while, noticed that it would error "no link found" for https links.

Fixed the quick-and-dirtiest way I know how -- just adding https links to the list.

It's possible that you'll eventually want to deal with more initial strings later, but I didn't want to go messing around in your codebase too much.  This works for me.

open only works for links that start with "http://"
extended to deal with "https://"