Replace Kernel.warn with $stderr.puts

My project's rake task doesn't show warnings so just print directly to
stderr

lib/specjour/rsync_daemon.rb

@@ -58,11 +58,12 @@ def command
     def check_config_version
       File.read(config_file) =~ /\A# (\d+.\d+.\d+)/
       if out_of_date? Regexp.last_match(1)
-        Kernel.warn <<-WARN
+        $stderr.puts <<-WARN
 
 Specjour has made changes to the way #{CONFIG_FILE_NAME} is generated.
 Back up '#{config_file}'
 and re-run the dispatcher to generate the new config file.
+
         WARN
       end
     end

spec/rsync_daemon_spec.rb

@@ -65,13 +65,13 @@
   describe "#check_config_version" do
     it "warns when the version is out of date" do
       stub(File).read { "# 0.0.0\n" }
-      mock(Kernel).warn(/made changes/)
+      mock($stderr).puts(/made changes/)
       subject.send(:check_config_version)
     end
 
     it "doesn't warn when the version isn't out of date" do
       stub(File).read { "# #{Specjour::RsyncDaemon::CONFIG_VERSION}\n" }
-      dont_allow(Kernel).warn
+      dont_allow($stderr).puts
       subject.send(:check_config_version)
     end
   end