ruby1.8 compatibility

lib/gollum/markup.rb

@@ -401,7 +401,7 @@ module Gollum
       end
 
       highlighted = begin
-        encoding ||= Encoding::UTF_8
+        encoding ||= 'utf-8'
         blocks.map { |lang, code| Pygments.highlight(code, :lexer => lang, :options => {:encoding => encoding.to_s}) }
       rescue ::RubyPython::PythonError
         []

test/test_markup.rb

@@ -432,7 +432,7 @@ context "Markup" do
     index.commit("Add alpha.jpg")
 
     page = @wiki.page("Bilbo Baggins")
-    rendered = Gollum::Markup.new(page).render(false, Encoding::UTF_8)
+    rendered = Gollum::Markup.new(page).render(false, 'utf-8')
     assert_equal output, rendered
   end