title: gulp minifies already minified file
body: <p>I try to minify separate .js-files with gulp. Like:</p>
  
  <pre><code>file_one.js --&gt; file_one.min.js
  file_two.js --&gt; file_two.min.js
  </code></pre>
  
  <p>It works the first time I execute gulp. But if I run it a second time it looks like this:</p>
  
  <pre><code>file_one.js 
  file_one.min.js
  file_one.min.min.js
  file_two.js
  file_two.min.js
  file_two.min.min.js
  </code></pre>
  
  <p>And it repeats that pattern every timme i execute gulp. How can I stop it from minify already minified js.</p>
  
  <p>I use the following code:</p>
  
  <pre><code>gulp.task('scripts', function() {
      return gulp.src('dest/*js')
          .pipe(rename({ suffix: '.min' }))
          .pipe(uglify())
          .pipe(gulp.dest('dest'));
  });
  </code></pre>