request the ical feed via https when the http call fails

Adding this because google calendar gives out an http url, but
redirects to https, which is not allowed by ruby's open-uri library.
So, when the http request fails, we automatically fall back to https.
accomplish the same thing with a single regex
Merge pull request #8 from sportngin/try-https-when-http-fails

Request the iCal feed via https when http fails