nailgun: use write_jar_script

Formula/nailgun.rb

@@ -5,16 +5,10 @@ class Nailgun < Formula
   url 'http://downloads.sourceforge.net/project/nailgun/nailgun/0.7.1/nailgun-src-0.7.1.zip'
   sha1 '70f2ae1faafe9cf060f2a44968960703475705e4'
 
-  def script; <<-EOS.undent
-    #!/bin/bash
-    exec java -server -jar "#{prefix}/nailgun-0.7.1.jar"
-    EOS
-  end
-
   def install
     system "make"
-    (bin/'ng-server').write script
-    bin.install 'ng'
-    prefix.install 'nailgun-0.7.1.jar'
+    bin.install "ng"
+    libexec.install "nailgun-#{version}.jar"
+    bin.write_jar_script libexec/"nailgun-#{version}.jar", "ng-server", "-server"
   end
 end