title: I keep getting the error: Error: Too many arguments provided to Query.startAt(). when using AngularFire2
body: <p>I have a simple function that accepts parameters and returns the dataset</p>
  
  <pre><code>search(searchValues , numOfItems, startKey?) {
      return this.db.collection('gppContract', ref =&gt; ref
      .where('financialYear', '==', searchValues.financialYear)
      .startAt(startKey)
      .orderBy('amount', 'desc')
      .limit(numOfItems + 1))
        .valueChanges();
  
  
    }
  </code></pre>
  
  <p>What am i doing wrong or missing? am at a loss here.</p>