Nah, 1.2.0 is the version of Jeykll Now - this is a Jeykll theme.
Basically it sounds like the OP has forked the repo, made a couple of changes and published them to GitHub Pages. GitHub Pages are powered by Jekyll behind the scenes, but I have no idea which exact version of Jeykll GitHub is using.
If the OP has installed Jeykll locally (using
gem install github-pages for example), then they can see which version of Jeykll they are using by running
gem list jeykll from the command line.