Add syntax highlighting for Dockerfile mode

Cask

@@ -2,5 +2,6 @@
 (source melpa)
 (source org)
 
+(depends-on "dockerfile-mode")
 (depends-on "htmlize")
 (depends-on "org-plus-contrib")

publish.el

@@ -27,6 +27,7 @@
 (require 'ox-publish)
 (require 'ox-rss)
 (require 'subr-x)
+(require 'dockerfile-mode)
 
 (defun publish-calculate-reading-time (buffer)
   "Calculate the amount of minutes it would take to read the contents of BUFFER."