title: Set gulp tasks depending on NODE_ENV
body: <p>Is there a way to specify a gulp task depending on the <code>NODE_ENV</code> that is set?</p>
  
  <p>For example in my <code>package.json</code> file, I have something like:</p>
  
  <pre><code>"scripts": {
      "start": "gulp"
   }
  </code></pre>
  
  <p>And I have multiple <code>gulp</code> tasks</p>
  
  <pre><code>gulp.task('development', function () {
     // run dev related tasks like watch 
  });
  
  gulp.task('production', function () {
     // run prod related tasks
  });
  </code></pre>
  
  <p>If I set <code>NODE_ENV=production npm start</code>, can I specify to only run <code>gulp production</code>? Or is there a better way to do this?</p>