title: gulp-concat does not concat one of my files on heroku
body: <p>I'm using gulp to generate a config.js file for angular, then use another gulp task to concat all .js files together, the gulp tasks look like this:</p>
  
  <pre><code>gulp.task('config', function() {
      var environment = process.env.NODE_ENV || 'development';
      gulp.src('public/config/' + environment + '.json')
          .pipe(ngConstant({
              name: 'app.config'
          }))
          .pipe(concat('public/js/config.js'))
          .pipe(gulp.dest('.'));
  });
  
  gulp.task('js', ['config'], function() {
      gulp.src('public/js/*.js')
          .pipe(concat('app.js'))
          .pipe(gulp.dest('public/dist'));
  });
  
  
  gulp.task('default', ['config', 'js']);
  </code></pre>
  
  <p>If I run gulp locally, everything works file. </p>
  
  <p>But when I push to heroku, using this post install script:</p>
  
  <pre><code>"postinstall": "bower install &amp;&amp; gulp"
  </code></pre>
  
  <p>I can see gulp run successfully, after adding some debug, I can see the config.js file is even created correctly, but the generated app.js does not include config.js. Can anyone suggest what might be wrong here?</p>
  
  <p><strong>UPDATE</strong>: I found it works if I do <code>gulp config &amp;&amp; gulp js</code> but not <code>gulp</code>, is this because gulp is async and config.js wasn't created when js job started to run? but i thought I have already specified the task dependencies?</p>