gulp 与 gulp-ruby-sass:错误:../style.css.map:3:1:未知单词

Getting a strange error using a basic gulp/express build watch.

目录布局

 project/
   - sass/
      - style.scss
   - gulpfile.js
   - index.html

Gulpfile.js

var gulp         = require('gulp'),
    sass         = require('gulp-ruby-sass'),
    autoprefixer = require('gulp-autoprefixer'),
    minifycss    = require('gulp-minify-css'),
    rename       = require('gulp-rename');

gulp.task('express', function() {
  var express = require('express');
  var app = express();
  app.use(require('connect-livereload')({port: 4002}));
  app.use(express.static(__dirname));
  app.listen(4000);
});

var tinylr;
gulp.task('livereload', function() {
  tinylr = require('tiny-lr')();
  tinylr.listen(4002);
});

function notifyLiveReload(event) {
  var fileName = require('path').relative(__dirname, event.path);

  tinylr.changed({
    body: {
      files: [fileName]
    }
  });
}

gulp.task('styles', function() {
    return gulp.src('sass/*.scss')
      .pipe(sass({ style: 'expanded', sourcemap: false }))
      .pipe(autoprefixer('last 2 version', 'safari 5', 'ie 8', 'ie 9', 'opera 12.1'))
      .pipe(gulp.dest('css'))
      .pipe(rename({suffix: '.min'}))
      .pipe(minifycss())
      .pipe(gulp.dest('css'));
});

gulp.task('watch', function() {
  gulp.watch('sass/*.scss', ['styles']);
  gulp.watch('*.html', notifyLiveReload);
  gulp.watch('css/*.css', notifyLiveReload);
});

gulp.task('default', ['styles', 'express', 'livereload', 'watch'], function() {

});

Style.scss

body { position: relative; }

快速服务器/livereload 工作正常，但是当它尝试编译样式表时出现此错误(即使使用 sourcemap: false)

gulp-ruby-sass: write style.css.map

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: <LOCAL_PATH_HERE>/style.css.map:3:1: Unknown word

.pipe(sass({ "sourcemap=none": true }))