Drupal 8 Grunt Livereload

Gruntfile.js

module.exports = function (grunt) {
    "use strict";
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        sass: {
            prod: {
                options: {
                    outputStyle: 'compressed'
                },
                files: {
                    'themes/custom/watchlearn/css/style.css': 'themes/custom/watchlearn/sass/style.scss',
                }
            },
            dev: {
                options: {
                    outputStyle: 'expanded'
                },
                files: {
                    'themes/custom/watchlearn/css/style.css': 'themes/custom/watchlearn/sass/style.scss',
                }
            }
        },
        watch: {
            options: {
                livereload: true,
            },
            css: {
                files: ['themes/custom/watchlearn/sass/**/*.scss',
                        'themes/custom/watchlearn/**/*.twig',
                        'themes/custom/watchlearn/**/*.js'],
                tasks: ['sass:dev'],
                options: {
                    spawn: false
                }
            },
            livereload: {
                options: {
                    livereload:true
                },
                files:[
                    'themes/custom/watchlearn/css/*.css',
                ]
            }
        }
    });

    // Load tasks...
    grunt.loadNpmTasks('grunt-sass');
    grunt.loadNpmTasks('grunt-contrib-watch');

    // Default task.
    grunt.registerTask('default', ['watch']);
};

package.json

{
  "name": "my-project",
  "version": "0.1.0",
  "devDependencies": {
    "grunt": "^0.4.1",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-sass": "^1.1.0",
    "node-sass": "^2.1.1"
  }
}