gulpfile.less.js

var gulp = require('gulp');
var less = require('gulp-less');
var sourcemaps = require('gulp-sourcemaps');
var LessPluginCleanCSS = require("less-plugin-clean-css"),
    cleancss = new LessPluginCleanCSS({advanced: true});
var LessPluginAutoPrefix = require('less-plugin-autoprefix'),
    autoprefix = new LessPluginAutoPrefix({browsers: ["last 2 versions"]});

gulp.task('default', function () {
  gulp.src('./less/project.less')
      .pipe(sourcemaps.init())
      .pipe(less({
        plugins: [autoprefix, cleancss]
      }))
      .pipe(sourcemaps.write())
      .pipe(gulp.dest('./css'));
});