Back in 2012, Matt Cutts, encouraged to use HTTP in concern to the security measures that Google take and invest the most.
Even though he is on a leave, he got his wish. And as of now, security is the top priority for Google to enhance the user experience and had officially announced HTTP as a ranking factor in Google Webmaster Central Blog on August 6, 2014.
They aren't saying you've to migrate your blog from HTTP to HTTPS, perhaps they have clearly mentioned that although it's a ranking factor for now, it is affecting fewer than 1% of total global searches.
Read More Regarding HTTPs Ranking Signal Update -> http://www.viralblogtips.com/https-as-ranking-factor/