title: Mongoose validation works for string but not for array of strings
body: <p>I'm trying to validate a field in my Schema to check if the string passed has a valid extension and if it is from a whitelisted host
  I'm using the <a href="https://github.com/leepowellcouk/mongoose-validator" rel="nofollow">mongoose-validator</a> lib to create my rules.</p>
  
  <p>The problem is, when the field is a String, it validates perfectly:</p>
  
  <pre><code>photos:  {type: String, 
            validate: [validate('isValidExtension'), validate('isValidHostname')]},
  </code></pre>
  
  <p>But what I really want is an Array of Strings:</p>
  
  <pre><code>photos: [{type: String, 
            validate: [validate('isValidExtension'), validate('isValidHostname')]}],
  </code></pre>
  
  <p>And, for some reason, it doesn't call the validation this way.</p>
  
  <p>I have another example where I'm using a similar validation, but instead of using an Array of Strings, I'm using an Array of Objects.</p>
  
  <p>Am I missing anything here?</p>