Try replacing the last few lines with the following
R.assign "content", content
R.eval "knitr::render_markdown(strict = TRUE)"
R.pull "(knitr::knit2html(text = content, fragment.only = TRUE))"
I think you need R.pull
to copy the contents of R output to Ruby. Moreover, I would recommend directly converting from Rmd to html. I have used this strategy successfully in working with Ruhoh which is another ruby based blogging platform.
UPDATE. It is very odd but using the extension rmd seems to conflict with md. I changed it randomly to ram
and jekyll seems to pick it up correctly. I am not sure why.