Dependency error... kramdown-math-MathJax

I got the following message trying to build my site:

Dependency Error: Yikes! It looks like you don't have kramdown-math-MathJax or one of its dependencies installed. In order to use Jekyll as currently configured, you'll need to install this gem. If you've run Jekyll with `bundle exec`, ensure that you have included the kramdown-math-MathJax gem in your Gemfile as well. The full error message from Ruby is: 'cannot load such file -- kramdown-math-MathJax' If you run into trouble, you can find helpful resources at! 
  Conversion error: Jekyll::Converters::Markdown encountered an error while converting '_posts/':
      Jekyll 3.8.5   Please append `--trace` to the `build` command 
                     for any additional information or backtrace. 

I have to remove the reference to MathJax as math engine from my _config.yml to make it work.

  math_engine: MathJax
  math_engine_opts: # more info:
    preview: false
    preview_as_code: false 

Does anyone know what is going on?


OK… I just figure it out… it was the caps on the MathJax… it should all in small letters mathjax. Funny thing it was working just fine till I update to kramdown 2.1.

How are you using Jekyll?
The last released version jekyll-3.8.5 has kramdown locked to the 1.x series. You shouldn’t be able to use kramdown-2.1 at all…

I’m using the master version

gem "jekyll", github: "jekyll/jekyll" # allow to build Jekyll faster.

because it’s decrease significantly the building time, as explained here: How I reduced my Jekyll build time by 61%

PS/ of course I’m not building it with gh-pages, but in travis.

Jekyll-4.0.0.pre.alpha1 has been released, along with a document detailing what to know when using the new version:

Besides, now that master is at a different version altogether, do note that your plugins may not work since they may still be locked to v3.x.y.

Oh great!

Thanks a lot for the info! I think I need it because I got another error today.