Fix "500: Encoding error" on blame view

This change forces encoding of source line data into UTF-8 and thus
fixes the encoding error at least partially. The issue is described in
https://gitlab.com/gitlab-org/gitlab-ce/issues/894

app/views/projects/blame/show.html.haml

@@ -30,5 +30,5 @@
                 %code
                   :erb
                     <% lines.each do |line| %>
-                      <%= highlight(@blob.name, line, true).html_safe %>
+                      <%= highlight(@blob.name, line.force_encoding("utf-8"), true).html_safe %>
                     <% end %>