remove RMarkdown from the linguist match list

Author: kivikakk

lib/github/markup/markdown.rb

@@ -31,7 +31,7 @@ class Markdown < Implementation
       def initialize
         super(
           /md|mkdn?|mdwn|mdown|markdown|litcoffee/i,
-          ["Markdown", "RMarkdown", "Literate CoffeeScript"])
+          ["Markdown", "Literate CoffeeScript"])
       end
 
       def load