I have patched your plugin to be able to use it with Redmine trunk @r2700. I'll paste the patch below, hoping that it does not get screwed up by the pre-tag handling.
I have bumped the version from 0.1.3 to 0.2.0 to reflect the changes...

Index: config/locales/en.yml
===================================================================
--- config/locales/en.yml   (revision 0)
+++ config/locales/en.yml   (revision 0)
@@ -0,0 +1,3 @@
+en:
+  burndown: "Burndown"
+  burndown_text_no_sprint: "There is no current Sprint for this Project"
Index: init.rb
===================================================================
--- init.rb (revision 221)
+++ init.rb (working copy)
@@ -9,11 +9,11 @@
   Project.class_eval { include ScrumAlliance::Redmine::CurrentVersionExtension }
 end
 
-Redmine::Plugin.register :burndown do
+Redmine::Plugin.register :redmine_burndown do
   name 'Redmine Burndown plugin'
   author 'Dan Hodos'
   description 'Generates a simple Burndown chart for using Redmine in Scrum environments'
-  version '1.1.3'
+  version '1.2.0'
 
   project_module :burndowns do  
     permission :show_burndown, :burndowns => :show, :public => true

HTH... ;)