Email Validation Jquery Validation

HTML

<script src="//cdn.jsdelivr.net/jquery.validation/1.15.0/jquery.validate.js"></script>
<link rel="stylesheet" href="//getbootstrap.com/dist/css/bootstrap.min.css">
<form id="checkform">
<input id="emailk" type="email" name="email">
</form>
<hr>
<p>Try to put first "abcc" and click outside field </p>
<p>then try to put "abcc@gmail" and click outside field </p>
<p>it will consider it a valid email but actually it is not.</p>

JavaScript

$(document).ready(function() {
jQuery.validator.addMethod("validate_email",function(value, element) {


       if(/^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/.test( value ))
        {
           return true;
        }
        else
        {
          return false;
        }    
  },"Please enter a valid Email.");

    $('#emailk').keyup(function(){
		$('#checkform').validate({
        rules:{
        email: {
                  validate_email: true
                },
        }

});
	 });
});