Update to jekyll-sass-converter to v1.2.0.

This version allows for users to set a custom output style in safe mode.
https://github.com/jekyll/jekyll-sass-converter/releases/tag/v1.2.0
https://github.com/jekyll/jekyll-sass-converter/compare/v1.1.0...v1.2.0
https://github.com/jekyll/jekyll-sass-converter/pull/16
Merge pull request #84 from github/sass

Update to jekyll-sass-converter to v1.2.0.