now Github pages :push task forces

Rakefile

@@ -235,7 +235,7 @@ multitask :push do
     message = "Site updated at #{Time.now.utc}"
     system "git commit -m \"#{message}\""
     puts "\n## Pushing generated #{deploy_dir} website"
-    system "git push origin #{deploy_branch}"
+    system "git push origin #{deploy_branch} --force"
     puts "\n## Github Pages deploy complete"
   end
 end