fix the issue on github #157.

directly force_encoding is wrong,
must detect the file string's encoding.
then force_encoding the string to it's encoding.
last convert it to utf-8.

app/helpers/commits_helper.rb

@@ -1,4 +1,5 @@
 module CommitsHelper
+  include Utils::CharEncode
   def diff_line(line, line_new = 0, line_old = 0)
     full_line = html_escape(line.gsub(/\n/, ''))
     color = if line[0] == "+"