Не работает плагин gulp-sourcemap

var gulp = require('gulp'); 
var less = require('gulp-less'); 
var concat = require('gulp-concat'); 
var uglify = require('gulp-uglify'); 
var cssmin = require('gulp-cssmin'); 
var autoprefixer = require('gulp-autoprefixer'); 
var browserSync = require('browser-sync'); 
var sourcemaps = require('gulp-sourcemaps'); 
var htmlmin = require('gulp-htmlmin'); 
 
 
 
var path = { 
 
	build: { 
		html: 'dist/', 
		js: 'dist/js', 
		css: 'dist/css', 
		img: 'dist/img', 
		fonts: 'dist/fonts' 
	}, 
 
	src: { 
		html: 'app/*.html', 
		js: 'app/js/*.js', 
		css: 'app/css/*.css', 
		img: 'app/img/**/*.*', 
		fonts: 'fonts/**/*.*' 
	}, 
 
	watch: { 
		html: 'app/*.html', 
		js: 'app/js/*.js', 
		less: 'app/less/**/*.less', 
		img: 'app/img/**/*.*', 
		fonts: 'fonts/**/*.*' 
	} 
} 
 
gulp.task('browser-sync', function() { 
    browserSync.init({ 
        server: { 
            baseDir: "dist/" 
        } 
    }); 
}); 
 
gulp.task('less', function() { 
	return gulp.src('app/less/styles.less') 
	.pipe(less()) 
	.pipe(gulp.dest('app/css/')) 
	.pipe(browserSync.reload({stream: true})) 
}) 
 
 
gulp.task('css', function() { 
	return gulp.src(path.src.css) 
	.pipe(concat('styles.css')) 
	.pipe(sourcemaps.init()) 
	.pipe(cssmin()) 
	.pipe(autoprefixer({ 
		browsers: ['last 4 versions'], 
		cascade: false 
	})) 
	.pipe(sourcemaps.write()) 
	.pipe(gulp.dest(path.build.css)) 
	.pipe(browserSync.reload({stream: true})) 
}) 
 
gulp.task('html', function() { 
	return gulp.src(path.src.html) 
	.pipe(htmlmin()) 
	.pipe(gulp.dest(path.build.html)) 
	.pipe(browserSync.reload({stream: true})) 
}) 
 
 
gulp.task('build', ['browser-sync'], function() { 
	gulp.watch(path.watch.less, ['less', 'css']); 
	gulp.watch(path.watch.html, ['html']) 
})