CSS prefixes do not appear when compiling with gulp-ruby-sass

I am using gulp-ruby-sass instead of gulp-sass for the pre-compilation of the scss code of my project. It turns out that I still have prefixes in my file .scss and following the way in which the mixins are declared

such as:

@mixin border-radius($radius) {
  -webkit-border-radius: $radius;
     -moz-border-radius: $radius;
      -ms-border-radius: $radius;
          border-radius: $radius;
}

You should produce something like:

.box {
  -webkit-border-radius: 10px;
  -moz-border-radius: 10px;
  -ms-border-radius: 10px;
  border-radius: 10px;
}

But I only get:

.box {
  border-radius: 10px;
}

Without the prefixes.

Does anyone else happen to him? Could it be that simply gulp-ruby-sass does not compile with the prefixes?

This way I have the tasks of gulp:

var gulp = require("gulp");
// Requires the gulp-sass plugin
var sass = require("gulp-ruby-sass");
// Requires browser-sync package for automatic browser refresh
var browserSync = require("browser-sync").create();

// Static Server + watching scss/html files
gulp.task("serve", ["sass"], function(){

  browserSync.init({
    server: "./src"
  });
  /**
  * Listens changes for all .scss files
  */
  gulp.watch("src/scss/*.scss", ["sass"]);
  /**
  * Listens changes for all .html files
  */
  gulp.watch("src/*.html").on("change", browserSync.reload);
  gulp.watch("src/en/*.html").on("change", browserSync.reload);
});

/**
 * Compile with gulp-ruby-sass
 */

gulp.task("sass", function () {
  return sass("src/scss/style.scss")
    .on("error", sass.logError)
    // Writes converted css to dest url
    .pipe(gulp.dest("src/css"))
    .pipe(browserSync.stream({match: "src/*.css"}))
});