As of maruku engine (the default), writing table like
maruku
surround text, etc. | Tables | Are | Cool | | ------------- |:-------------
Adding only markdown: redcarpet into _config.yml is not enough, It's also need the extensions part, e.g.
markdown: redcarpet
_config.yml
extensions
markdown: redcarpet redcarpet: extensions: ["no_intra_emphasis", "fenced_code_blocks", "autolink", "tables", "with_toc_data"]