Gulp错误：-您是否忘记了异步完成信号？

Question

运行gulp文件时出现以下错误：

“默认”在64毫秒后错误[16:02:03]以下任务没有 完成：发球，无礼[16:02:03]您忘记发信号了吗？ 完成吗？

代码是：

var gulp = require('gulp')
var browserSync = require('browser-sync').create()
var sass = require('gulp-sass')

gulp.task('compile-sass', function() {
    return gulp.src(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'])
    .pipe(sass())
    .pipe(gulp.dest('src/css'))
    .pipe(browserSync.stream())

})

gulp.task('move-js', function() {
    return gulp.src(['node_modules/bootstrap/dist/js/bootstrap.min.js', 'node_modules/jquery/dist/jquery/jquery.min.js'])
    .pipe(gulp.dest('src/js'))
    .pipe(browserSync.stream())

})

//run sass when serve runs
//run server
//watch for any changes in src/scss folder and reload the browser
//also watch for sass changes
//watch for html changes
gulp.task('launch-server', ['compile-sass'], function() {
    browserSync.init({
        server: "./src"
    })
    gulp.watch(['node_modules/bootstrap/scss/bootstrap.scss', 'src/scss/*.scss'],['compile-sass'])
    gulp.watch("src/*.html").on('change', browserSync.reload)


})

//run gulp
//launch server and browser
//execute js task
gulp.task('default', ['move-js', 'launch-server'])