I know it’s a bit late, but I had the same problem, so I wrote a minor fix, that replaces the img with the svg … hope this helps;)
It’s important, that when you create your diagram, it has to be exportet as an svg.
jQuery(document).ready(function($) {
$('img[title="drawit diagram"]').each(function(index){
var diagram = $(this);
var diagramImg = diagram.attr('title', 'drawit diagram');
var diagramImgSrc = diagramImg.context.src;
var diagramClasses = diagramImg.context.className;
var diagramWidth = diagramImg.context.clientWidth;
var container = $('<div class="drawio-diagram ' + diagramClasses + '" style="width:' + diagramWidth + 'px"></div>');
container.insertAfter(diagram);
container.load(diagramImgSrc);
diagram.remove();
});
});