grunt sprite Fatal error: grunt.sprite requires a src, dest (img), and destCss property

Question

I am trying run grunt sprite on my project: https://github.com/Ensighten/grunt-spritesmith

all folders and files exists and are there, any help?

after run on terminal: grunt sprite

I got this. Fatal error: grunt.sprite requires a src, dest (img), and destCss property

my grunt:

/sprite ===============================
                var sprite;
    config.sprite = sprite = {};

      // Configure grunt 
      sprite.dist ={
        sprite:{
          all: {
             src: 'public/images/*.png',
            dest: 'public/images/sprite/spritesheet.png',
            destCss: 'sass/sprites.css'
          }
        }
      };