Bootstrap 3 to 4 Migration in File Upload button and Input size issue-Twitter bootstrap

$(document).ready( function() {
    	$(document).on('change', '.btn-file :file', function() {
		var input = $(this),
			label = input.val().replace(/\/g, '/').replace(/.*//, '');
		input.trigger('fileselect', [label]);
		});

		$('.btn-file :file').on('fileselect', function(event, label) {
		    
		    var input = $(this).parents('.input-group').find(':text'),
		        log = label;
		    
		    if( input.length ) {
		        input.val(log);
		    } else {
		        if( log ) alert(log);
		    }
	    
		});
		function readURL(input) {
		    if (input.files && input.files[0]) {
		        var reader = new FileReader();
		        
		        reader.onload = function (e) {
		            $('#img-upload').attr('src', e.target.result);
		        }
		        
		        reader.readAsDataURL(input.files[0]);
		    }
		}

		$("#imgInp").change(function(){
		    readURL(this);
		}); 	
	});

.btn-file {
    position: relative;
    overflow: hidden;
}
.btn-file input[type=file] {
    position: absolute;
    top: 0;
    right: 0;
    min-width: 100%;
    min-height: 100%;
    font-size: 100px;
    text-align: right;
    filter: alpha(opacity=0);
    opacity: 0;
    outline: none;
    background: white;
    cursor: inherit;
    display: block;
}

#img-upload{
    width: 100%;
}

<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!------ Include the above in your HEAD tag ---------->

<div class="container">
<div class="col-md-6">
    <div class="form-group">
        <label>Upload Image</label>
        <div class="input-group">
            <span class="input-group-btn">
                <span class="btn btn-default btn-file">
                    Browse… <input type="file" id="imgInp">
                </span>
            </span>
            <input type="text" class="form-control" readonly>
        </div>
        <img id='img-upload'/>
    </div>
</div>
</div>