Grunt在观看时没有做出改变

Question

Grunt说等待......但是在观看时不会改变sass。每次我希望它运行和改变时，我必须在命令行上运行grunt。我最需要更新的是css的sass。但它不起作用。请帮忙。

module.exports = function (grunt) {
grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),

    // package options
    express: {
        server: {
            options: {
                port: 3000,
                hostname: 'localhost',
                bases: 'public' // the 'public' folder for your project
            }
        }
    },
    jshint: {
        options: {
            jshintrc: '.jshintrc' // jshint config file
        },
        all: [
            'Gruntfile.js',
            'js/*.js'
        ]
    },
    concat: {
        basic: {
            src: [
                'bower_components/jquery/dist/jquery.js',
                'bower_components/foundation/js/foundation/foundation.js',
                'dev/js/jquery.royalslider.custom.min.js',
                'dev/js/royalslider.js',
                'dev/js/megamenu_plugins.js',
                'dev/js/megamenu.min.js',
                'dev/js/megamenu.js',
                'dev/js/app.js'
            ],
            dest: 'dev/tmp/app.js'
        },
        extras: {
            src: [
                'bower_components/modernizr/modernizr.js'
            ],
            dest: 'dev/tmp/modernizr.js'
        }
    },
    sass: {
        options: {
            includePaths: ['bower_components/foundation/scss']
        },
        dist: {
            options: {
                outputStyle: 'compressed'
            },
            files: {
                'public/build/css/app.min.css': 'dev/scss/app.scss'
            }
        }
    },
    imagemin: {
        dynamic: {
            files: [{
                expand: true,
                cwd: 'dev/img/',
                src: ['**/*.{png,jpg,gif}'],
                dest: 'public/build/img/'
            }]
        }
    },
    uglify: {
        build: {
            files: {
                'public/build/js/modernizr.min.js': 'dev/tmp/modernizr.js',
                'public/build/js/app.min.js': 'dev/tmp/app.js'
            }
        }
    },
    clean: {
        dist: [
            'tmp/**',
            'public/build/img/**'
        ]
    },


    watch: {
        grunt: {
            files: ['Gruntfile.js']
        },
        css: {
                            files: ['scss/*.scss'],
                            tasks: ['newer:sass'],
                            options: {
                                    spawn: false
                            }
                    },
        js: {
            files: [
                'js/*.js'
            ],
            tasks: ['newer:concat', 'newer:uglify'],
            options: {
                livereload: true,
                atBegin: true
            }
        },
        imagemin: {
            files: [
                'img/**'
            ],
            tasks: ['newer:imagemin'],
            options: {
                livereload: true,
                atBegin: true
            }
        }
    }
});

    // Load tasks
grunt.loadNpmTasks('grunt-sass');
grunt.loadNpmTasks('grunt-contrib-clean');
grunt.loadNpmTasks('grunt-contrib-jshint');
grunt.loadNpmTasks('grunt-contrib-concat');
grunt.loadNpmTasks('grunt-contrib-uglify');
grunt.loadNpmTasks('grunt-notify');
grunt.loadNpmTasks('grunt-contrib-watch');
grunt.loadNpmTasks('grunt-contrib-imagemin');
grunt.loadNpmTasks('grunt-express');
    grunt.loadNpmTasks('grunt-newer');

    // Register default tasks
grunt.registerTask('build', ['sass']);
grunt.registerTask('default', ['build','watch']);
}