replace all backticks inside code blocks with nothing

[gumaerc]

Pre-Flight checklist

• [ ] Testing
  • [ ] Code is tested
  • [ ] Changes have been manually tested

What are the relevant tickets?

Part of https://github.com/mitodl/ocw-hugo-themes/issues/704

What's this PR do?

This PR adds functionality to the codeblockfix rule to ensure that elements that normally produce inline code blocks (code, kbd, tt, samp) do not do so when included inside an element that produces a multi-line code block. This is done by simply replacing backticks inside multi-line code blocks with nothing. This PR also updates the version of Node used in the CI Github Actions runner as it was causing a test to fail.

How should this be manually tested?

• Read the readme if you've never used ocw-to-hugo before and make sure you're set up to download courses from S3
• Place the following in private/courses.json:

  {
  "courses": [
      "15-071-the-analytics-edge-spring-2017",
      "2-s998-marine-autonomy-sensing-and-communications-spring-2012",
      "6-0001-introduction-to-computer-science-and-programming-in-python-fall-2016",
      "6-828-operating-system-engineering-fall-2012",
      "6-s096-effective-programming-in-c-and-c-january-iap-2014"
  ]
  }

• Run node . -i private/ -o private/output --courses private/courses.json --download --rm on master
• Run node . -i private/ -o private/test--courses private/courses.json --download --rm on cg/remove-nested-code-blocks
• Use a diff tool such as Meld to compare private/output and private/test and verify that backticks inside code blocks have been properly removed