Fix for upcoming t.co length changes

Twitter is going to be extending the maximum length of t.co wrapped links from 20 to 22 characters for non-https URLs, and 21 to 23 characters for https URLs.

This pull request updates the short_url_length and short_url_length_https options to match the coming t.co update mentioned here: https://dev.twitter.com/blog/upcoming-tco-changes