title: lunr is not returning exact matching as top priority
body: <p>Am using <code>lunr (elastic lunr0.9.5)</code> as search engine in web browser.
  It  is simple and very fast as well. but it is not listing exactly matched object in first position when it have more.</p>
  
  <p><strong>My lunr Configuration in Typescript</strong></p>
  
  <pre><code>this.lunrIndex = lunr(function () {
                  this.field('itemId');
                  this.field('name');
                  this.ref('itemId');
                  this.pipeline.remove(lunr.stemmer)
              })
  </code></pre>
  
  <p>When i search <code>pan d ca</code> text it is returning,</p>
  
  <pre><code>[{
      "ref": "PANCOR DSR CAPSULE 10''S",
      "score": 0.01674628244112235
    },
    {
      "ref": "PANLID DSR CAPSULE 10''S",
      "score": 0.01674628244112235
    },
    {
      "ref": "PANSIO DSR CAPSULE 10''S",
      "score": 0.01590146213665648
    },
    {
      "ref": "PANLIFE DSR CAPSULE 10''S",
      "score": 0.015507241586286287
    },
    {
      "ref": "PANSEC DSR CAPSULE 10''S",
      "score": 0.014526355502926632
    },
    {
      "ref": "PAN D CAPSULE 10''S",
      "score": 0.011554433713104873
    }
    ]
  </code></pre>
  
  <p>Lunr trimming may be one of reason for above result, so i removed <code>lunr.trimmer</code> from its pipeline execution and still it giving the same result.</p>
  
  <p>The above result shows, exact matching string(<code>PAN D C</code>) gets lower score(<code>0.011554433713104873</code>). am i missed any configuration here ?</p>
  
  <p><strong>I need the exact matching string should get highest score than others, How can i achieve that ?</strong></p>