Fix commas in code blocks of markdown (#20286)
Fix commas in code blocks of markdown (#20286)

* Fix commas in code blocks of markdown

If not specified, the parameter to Array.join is treated as ',' which resulted in commas being matched as a character that needs to be replaced by `escape-html.js` (but without a replacement specified, it was being rendered as the string 'undefined').

* chore: format

Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

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