title: Algolia helper searcher method Filter doesn't filter strings but filters numericals only
body: <p>I'm using Algolia-helper-swift [0.1] with Algolia-client-swift [3.7] since im using xcode 7.3.1 and swift 2.0+ and my json structure snippet is as follows</p>
  
  <pre><code> "-KTKNoEhrdaBShtXJGM8" : {
  "Book_name" : "Hello World",
  "Book_price" : 7273,
  "uploaded_by" : "John" }
  </code></pre>
  
  <p>Trial 1</p>
  
  <pre><code>{
    "params": "facetFilters=[]&amp;filters=Book_price%3E0%20AND%20uploaded_by:John&amp;hitsPerPage=8&amp;page=0&amp;query=&amp;restrictSearchableAttributes=[%22Book_name%22]"
  }
  </code></pre>
  
  <p>Trial 2</p>
  
  <pre><code>{
    "params": "facetFilters=[]&amp;filters=Book_price%3E0%20AND%20uploaded_by:%22John%22&amp;hitsPerPage=8&amp;page=0&amp;query=&amp;restrictSearchableAttributes=[%22Book_name%22]"
  }
  </code></pre>
  
  <p>Trial 3</p>
  
  <pre><code>{
    "params": "facetFilters=[]&amp;filters=Book_price%3E0&amp;hitsPerPage=8&amp;page=1&amp;query=&amp;restrictSearchableAttributes=[%22Book_name%22]"
  }
  </code></pre>
  
  <p>Trial 4</p>
  
  <pre><code>{
        "params": "facetFilters=[]&amp;filters=uploaded_by:%22John%22&amp;hitsPerPage=8&amp;page=0&amp;query=&amp;restrictSearchableAttributes=[%22Book_name%22]"
      }
  </code></pre>
  
  <p>The Trial 1,2 &amp; 4 don't work returns me 0 results/hits
  the third however works but its a numerical logic.
  Please if someone could help me with this it would be great.</p>