gulp-sass: not working with gulp 4.0

Task did not finish Starting gulpSass…

var gulp = require('gulp');
var sass = require('gulp-sass');

var paths = {
  sass:    'src/css/**/*.scss',
 };
gulp.task('sass', function () {
  return sass(paths.sass)
    .on('error', sass.logError)
    .pipe(gulp.dest('src/css'));
});
function watch() {
  livereload.listen();
  ...
  gulp.watch(paths.sass, sass);
}

gulp.task('build',  gulp.parallel(sass, ... watch));

gulp.task('default', gulp.series('build'));