Minified 0 images in grunt imagemin:dynamic

I'm trying to minify the images but it says:

Minified 0 images.

If I change the value of the src property to: ['**/.*{png,gif,jpg,jpeg}'] - it minifies the node_modules folder and the images in there.

The Gruntfile.js is in the same path as the folder img.

Some help please?

        imagemin: {
            dynamic: {
                files: [{
                    expand: true,
                    cwd: './',
                    src: 'img/*.{png, gif, jpg, jpeg}',
                    dest: 'dist/'
                }]
            }
        },