Why grunt slim write file only in minify version

[Mario]

I think I wrote the instructions is correctly in gruntfile.js.
But the files are written without indentation, then all on a single line.

Thanks for time and help ;-)

dist: {
    files: [{
      expand: true,
      cwd: '<%= project.assets %>/slim/',
      src: [
        // first level
        '_.slim',
        // template
        'template-parts/_.slim',
        // head
        'template-parts/head/_.slim',
        // footer
        'template-parts/footer/_.slim',
        // content
        'template-parts/content/_.slim',
        'template-parts/content/slide/_.slim',
        'template-parts/content/float/_.slim',
        'template-parts/content/header-interni/_.slim',
        'template-parts/content/widget/_.slim',
        'template-parts/content/tab-page/_.slim',
        'template-parts/content/flussi/_.slim',
        'template-parts/content/area-riservata/_.slim'
      ],
      dest: '../',
      ext: '.php'
    }]
  },

[Mario]

Non avevo settato il parametro pretty: true, sotto option

module.exports = {

dist: { // Another target
options: { // Target options
pretty: true,
},
files: [{
expand: true,
cwd: '<%= project.assets %>/slim/',
src: [
// first level
'.slim',
// template
'template-parts/.slim',
// head
'template-parts/head/.slim',
// footer
'template-parts/footer/.slim',
// content
'template-parts/content/*.slim',
],
dest: '../',
ext: '.php'
}]
},

};