bump github-linguist dependency to work around transitive dep issues
bump github-linguist dependency to work around transitive dep issues

github-linguist 2.12.0 depends on an old version of pygments.rb which
depends on an old version of yajl-ruby which does not compile on ruby 2.4

gjtorikian/html-pipeline,jch/html-pipeline,gjtorikian/html-pipeline,jch/html-pipeline