title: gulp Task is not in your gulpfile
body: <p>new to node.js, trying to use gulp. I got this error: </p>
  
  <pre><code>Task 'styles' is not in your gulpfile
  </code></pre>
  
  <p>I see it is a very common error, what can cause it? 
  This is my code.</p>
  
  <p>Both auto-prefixer and gulp are in my <code>package.json</code> file</p>
  
  <p>the file name is <code>autoprefixer.js</code></p>
  
  <pre><code>var gulp = require('gulp');
  var autoprefixer = require('gulp-autoprefixer');
  
  
  gulp.task('styles',function(){
      return gulp.src('css/style.css')
      .pipe(autoprefixer())
      .pipe(gulp.dest('build'))
  });
  </code></pre>
  
  <p>what can be the problem?</p>