latex-publish.el: latexmk command must not contain line breaks

latex-publish.el

 ;; Override the default LaTeX publishing command.
 (setq org-latex-pdf-process
-      (list "latexmk --shell-escape -f -pdf -%latex -interaction=nonstopmode
--output-directory=%o %f"))
+      (list
+       "latexmk --shell-escape -f -pdf -%latex -interaction=nonstopmode -output-directory=%o %f"))
 
 ;; Preserve user-defined labels during the export to PDF via LaTeX.
 (setq org-latex-prefer-user-labels t)