Gulp unCSS问题：以下任务未完成：uncss和是否忘记了异步完成信号？

Question

我对gulp-uncss有疑问 这是

$ gulp uncss
[14:00:53] Using gulpfile c:\users\Chandan\desktop\strap-gm\gulpfile.js
[14:00:53] Starting 'uncss'...
[14:02:01] The following tasks did not complete: uncss
[14:02:01] Did you forget to signal async completion?

版本：

$ gulp -v
[14:02:48] CLI version 2.0.1
[14:02:48] Local version 4.0.0

这是我的gulpfile.js文件

//Include Gulp
var gulp = require('gulp');
//Include plugins
var uncss = require('gulp-uncss');
var rename = require('gulp-rename');

//Uncss task
gulp.task('uncss', function() {

gulp.src('dist/css/bootstrap.min.css')       .pipe(uncss({          html: 

    ["http:\/\/localhost\/mysite\/wordpress\/2018\/11\/welcome-to-the-gutenberg-editor\/", "http:\/\/localhost\/mysite\/wordpress\/tag\/gulp\/"]     

  }))        
.pipe(rename({suffix: '.clean'}))

.pipe(gulp.dest('dist/css/'));

});

之前，成功完成了，但是这次没有。任何帮助请。