add MathJax as global for ChallengePanel test
add MathJax as global for ChallengePanel test

kevinnorris/arcade-mode,kevinnorris/arcade-mode,freeCodeCamp/arcade-mode,freeCodeCamp/arcade-mode,kevinnorris/arcade-mode,freeCodeCamp/arcade-mode,freeCodeCamp/arcade-mode,kevinnorris/arcade-mode