add missing step for gem-based theme conversion (#6802)
add missing step for gem-based theme conversion (#6802)

Merge pull request 6802
x-way/jekyll,tillgrallert/jekyll,ryanshaw/jekyll,fulldecent/jekyll,Strangehill/jekyll,ryanshaw/jekyll,x-way/jekyll,Strangehill/jekyll,chrisfinazzo/jekyll,ryanshaw/jekyll,jaybe-jekyll/jekyll,fulldecent/jekyll,getandpost/jekyll.github.io,getandpost/jekyll.github.io,ryanshaw/jekyll,jekyll/jekyll,jaybe-jekyll/jekyll,Strangehill/jekyll,fulldecent/jekyll,Strangehill/jekyll,tillgrallert/jekyll,x-way/jekyll,jekyll/jekyll,fulldecent/jekyll,jaybe-jekyll/jekyll,chrisfinazzo/jekyll,jaybe-jekyll/jekyll,tillgrallert/jekyll,Strangehill/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,getandpost/jekyll.github.io,x-way/jekyll,chrisfinazzo/jekyll,tillgrallert/jekyll,jekyll/jekyll,yhironaka/yhironaka.github.io,jekyll/jekyll