I'm trying to use `dot` inside `org-mode` and having no luck, because when
I evaluate

    (org-babel-do-load-languages
     'org-babel-load-languages
     '((dot . t)))

it tries to require `ob-graphviz-dot` -- unsuccessfully.

    Debugger entered--Lisp error: (file-error "Cannot open load file" "No
such file or directory" "ob-graphviz-dot")
      require(ob-graphviz-dot)

I can't find `ob-graphviz-dot` anywhere.