Я использовал postcss-less
с autoprefixer
const gulp = require('gulp');
const postcss = require('gulp-postcss');
const syntax = require('postcss-less');
const autoprefixer = require('autoprefixer');
gulp.task('default', () =>
gulp.src('less/*.less')
.pipe(postcss([
autoprefixer({ browsers: ['last 2 versions'] })
], { syntax }))
.pipe(gulp.dest('build/less'))
);