Error installing jekyll: ERROR: Failed to build gem native extension

Solution re-install ruby with rubyinstaller-devkit-2.5.5-1-x64

and issue

gem install bundler

gem install jekyll

Although they made the Ruby+DevKit an "optional" download for the RubyInstaller on Windows, if you plan to install gems, it is practically a necessity. A large percentage of the most popular gems are C extension that will need built on your machine when being installed.

The DevKit is a handy toolchain that supplies everything you need for this to be done, automatically without you needed to do anything more than type gem install XXXXX. Without it, you either cannot use C extension gems, or must have already installed MSYS and MingW, have them configured properly, which is all not a user-friendly experience, even for those who familiar with the process.

So even if DevKit is optional, it is still required to make the most of Ruby on Windows.