title: schema builder laravel migrations unique on two columns
body: <p>How can I set a unique constraints on two columns? </p>
  
  <pre><code>class MyModel extends Migration {
    public function up()
    {
      Schema::create('storage_trackers', function(Blueprint $table) {
        $table-&gt;increments('id');
        $table-&gt;string('mytext');
        $table-&gt;unsignedInteger('user_id');
        $table-&gt;engine = 'InnoDB';
        $table-&gt;unique('mytext', 'user_id');
      });
    }
  }
  
  MyMode::create(array('mytext' =&gt; 'test', 'user_id' =&gt; 1);
  // this fails??
  MyMode::create(array('mytext' =&gt; 'test', 'user_id' =&gt; 2);
  </code></pre>