npm install --save-dev gulp-babel babel-core babel-preset-env

var gulp           = require('gulp'),
    babel          = require('gulp-babel'),
    uglify         = require('gulp-uglify');

gulp.task('build', function() {

    //.. другие подзадачи

    var buildJs = gulp.src([
        'app/js/scripts.min.js',
    ])
        .pipe(babel({
            presets: ['env']
        }))
        .pipe(uglify()) // Теперь это работает
        .pipe(gulp.dest('dist/js'));

});

let gulp = require("gulp");
let rename = require("gulp-rename");
let uglify = require('gulp-uglify-es').default;

gulp.task("uglify", function () {
    return gulp.src("lib/bundle.js")
        .pipe(rename("bundle.min.js"))
        .pipe(uglify(/* options */))
        .pipe(gulp.dest("lib/"));
});