Broken master docs lint

Job #562215156 failed for 8518daab:

  doc/development/api_styleguide.md
 179:1  error  Syntax highlighting hint        gitlab.CodeblockFences 
               "```rb" must be one of: yaml,                          
               ruby, plaintext, markdown,                             
               javascript, shell, golang,                             
               python, dockerfile, or                                 
               typescript.                                            
✖ 1 error, 0 warnings and 0 suggestions in 1411 files.