plugins: add jekyll target blank

[plowsof]

closes #1921 , closes #2118, closes #2233, closes #2379

here i am adding the minimum requirements to make the plugin work, namely the ruby bump

• ruby version changes
  • getmonero is using 3.0.2 to generate (i have confirmed this), netlify previews should mirror this so we can see if deployment will work.
  • 3.0.0 is the minimum required version for this plugin

to confirm the Gemfile.lock changes, please add gem jekyll-target-blank to your Gemfile then run bundle install , note the changes in Gemfile.lock after.

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