use grit to get the file's mime type, as suggested.

http://github.com/github/gollum/commit/6de9ddfd3f79a9cb320aab3c43b8e0a912107b2e#commitcomment-137656

HISTORY.md

@@ -8,6 +8,7 @@
 * Minor Enhancements
   * Support a `:gollum_path` Sinatra setting for `Precious::App`
   * Add Wiki#size to efficiently count pages without loading them.
+  * Add the correct content type when serving files from the frontend.
 * Bug Fixes
   * Increase minimum Sanitize version requirement to 1.1.0.
     1.0.x versions of Sanitize require Hpricot instead of Nokogiri

lib/gollum/file.rb

@@ -33,6 +33,11 @@ module Gollum
     # Public: The String path of the file.
     attr_reader :path
 
+    # Public: The String mime type of the file.
+    def mime_type
+      @blob.mime_type
+    end
+
     #########################################################################
     #
     # Internal Methods

lib/gollum/frontend/app.rb

@@ -141,7 +141,7 @@ module Precious
         @content = page.formatted_data
         mustache :page
       elsif file = wiki.file(name)
-        content_type MIME::Types.type_for(name).to_s
+        content_type file.mime_type
         file.raw_data
       else
         @name = name