title: Swagger @ApiModelProperty required field seems to get ignored (version 1.3.6)
body: <p>Required field is ignored and doesn't get generated.
  For example for property <code>a</code></p>
  
  <pre><code>import javax.xml.bind.annotation.XmlRootElement;
  import javax.xml.bind.annotation.XmlAccessType;
  import javax.xml.bind.annotation.XmlAccessorType;
  import javax.xml.bind.annotation.XmlElement;
  import javax.xml.bind.annotation.XmlTransient;
  
  import com.wordnik.swagger.annotations.ApiModel;
  import com.wordnik.swagger.annotations.ApiModelProperty;
  
      @XmlRootElement
      @XmlAccessorType(XmlAccessType.FIELD)
      @ApiModel( value = "aaa")
      public class A implements IA
      {
          @ApiModelProperty( value = "bla", required = true )
          @XmlElement(name="a")
          private String a;
  
  
           public String getC() { return "kkk";};
  }
  </code></pre>