Switch to HTTPS

Hi,

I started having some problems with my program that connects to Twitter. I'm not sure of the source of the problem, but switching to HTTPS and re-authenticating seems to have fixed the problem. (In fact, using the same credentials/tokens and updating the :ORIGIN-URI in the config also seems to have worked.)

In any case, we're likely to need to use HTTPS whether it was the source of this problem or not, so this pull request covers the 3 URLs that I updated to get it working.

(Feel free to ignore this pull request and just update the 3 http lines in twitter-vars.lisp if you prefer.)

Many thanks,

    Geoff