fix gulp build

gulpfile.js

@@ -17,11 +17,42 @@ var uglify       = require('gulp-uglify');
 
 var imagemin     = require('gulp-imagemin');
 
-gulp.task('serve', ['sass', 'imagemin', 'js'], function() {
+gulp.task('js', function () {
+  return gulp.src('src/**/*.js', {read: false})
+    .pipe(sourcemaps.init({loadMaps: true}))
+    .pipe(tap(function (file) {
+      gutil.log('bundling ' + file.path)
+      file.contents = browserify(file.path, {debug: true}).bundle()
+    }))
+    .pipe(streamify(babel({ presets: ['es2015', 'es2017'] })))
+    .pipe(buffer())
+    .pipe(uglify())
+    .pipe(sourcemaps.write('./'))
+    .pipe(gulp.dest('dist'))
+    .pipe(browserSync.stream());
+})
 
-    browserSync.init({
-        server: "./"
-    })
+gulp.task('sass', function() {
+  return gulp.src("src/scss/main.scss")
+    .pipe(sass())
+    .on('error', gutil.log)
+    .pipe(autoprefixer({ browsers: ['last 3 versions'], cascade: false }))
+    .pipe(gulp.dest("dist/css"))
+    .pipe(browserSync.stream());
+})
+
+gulp.task('imagemin', function() {
+  gulp.src('src/img/**/*')
+    .pipe(imagemin())
+    .pipe(gulp.dest('dist/img'))
+})
+
+gulp.task('cleanUp', function() {
+  del.sync('dist/*')
+})
+
+gulp.task('serve', ['build'], function() {
+    browserSync.init({server: "./"})
 
     gulp.watch("src/scss/*.scss", ['sass']);
     gulp.watch("src/js/*.js", ['js']);
@@ -29,38 +60,5 @@ gulp.task('serve', ['sass', 'imagemin', 'js'], function() {
     gulp.watch("./*.html").on('change', browserSync.reload);
 })
 
-gulp.task('js', function () {
-  return gulp.src('src/**/*.js', {read: false})
-             .pipe(tap(function (file) {
-                gutil.log('bundling ' + file.path)
-                file.contents = browserify(file.path, {debug: true}).bundle()
-              }))
-              .pipe(streamify(babel({ presets: ['es2015'] })))
-              .pipe(buffer())
-              .pipe(sourcemaps.init({loadMaps: true}))
-              .pipe(uglify())
-              .pipe(sourcemaps.write('./'))
-              .pipe(gulp.dest('dist'))
-              .pipe(browserSync.stream());
-})
-
-gulp.task('sass', function() {
-    return gulp.src("src/scss/main.scss")
-               .pipe(sass())
-               .on('error', gutil.log)
-               .pipe(autoprefixer({ browsers: ['last 3 versions'], cascade: false }))
-               .pipe(gulp.dest("dist/css"))
-               .pipe(browserSync.stream());
-})
-
-gulp.task('imagemin', function() {
-  gulp.src('src/img/**/*')
-      .pipe(imagemin())
-      .pipe(gulp.dest('dist/img'))
-})
-
-gulp.task('cleanUp', function() {
-  del.sync('dist/*')
-})
-
-gulp.task('default', ['cleanUp', 'serve']);
+gulp.task('build',   ['cleanUp', 'sass', 'imagemin', 'js']);
+gulp.task('default', ['serve']);