The svg.import.js plugin is obsolete as of SVG.js v2 and up, as stated here:
This is now built-in with the draw.svg() method. Here is an example in the docs:
However, you will need to load the SVG data, not a url. You can however load an external file using ajax and pass the file's contents to the SVG.js instance. Something like:
var ajax = new XMLHttpRequest()
ajax.open('GET', 'your/file.svg', true)
ajax.send()
ajax.onload = function(e) {
draw.svg(ajax.responseText)
}
Note: if you are loading files from Inkscape, it's safer to use the Plain SVG format.