Use Pathname methods instead of system method or File one

lib/tasks/clean.rake

@@ -1,6 +1,6 @@
 desc "clean all files/directories in tmp/ directory (use carefully)"
 task :clean do
-  tmp_directory = File.join(Rails.root, "tmp")
-  system("rm -rf #{tmp_directory}")
-  system("mkdir #{tmp_directory}")
+  tmp_directory = Rails.root.join("tmp")
+  tmp_directory.rmtree
+  tmp_directory.mkdir
 end