gulp minify sass to css

'use strict';
 
var gulp = require('gulp');
var sass = require('gulp-sass');
var watch = require('gulp-watch');
var concat = require('gulp-concat');
var cleanCSS = require('gulp-clean-css');

sass.compiler = require('node-sass');
 
gulp.task('sass', function () {
  return gulp.src('./src/sass/**/*.scss')
    .pipe(sass({outputStyle:"compressed"}).on('error', sass.logError))
    .pipe(concat('style.min.css'))
    .pipe(cleanCSS({compatibility: 'ie8'}))
    .pipe(gulp.dest('./assets/css'));
});
 
gulp.task('watch', function () {
	gulp.watch('./src/sass/**/*.scss', gulp.series(['sass']));
});

gulp.task("default", gulp.series('watch'));