remove closure_jar parameter from Gruntfile.js

Apparently it was forgotten to remove this from the template Gruntfile.js.
The closure_jar parameter has been removed from amberc a long time ago.

root/Gruntfile.js

@@ -28,8 +28,7 @@ module.exports = function (grunt) {
         amberc: {
             options: {
                 amber_dir: path.join(__dirname, "bower_components", "amber"),
-                library_dirs: ['src', 'bower_components/amber/contrib/src'],
-                closure_jar: ''
+                library_dirs: ['src', 'bower_components/amber/contrib/src']
             },
             all: {
                 src: [