feat: send XMLHttpRequest as second param for onError

Currently the `onError` callback only has the `req.statusText` field,
as param.

Would be useful to have the XMLHttpRequest object instance along
with the req.statusText, so we are able to consume all the details
from the request, the response (ArrayBuffer) for instance.

When available the XMLHttpRequest instance used in the request
is sent as second param for the `onError` callback.

src/index.d.ts

@@ -27,7 +27,7 @@ declare namespace printJS {
     css?: string | string[];
     style?: string;
     scanStyles?: boolean;
-    onError?: (error: any) => void;
+    onError?: (error: any, xmlHttpRequest?: XMLHttpRequest) => void;
     onPrintDialogClose?: () => void;
     onIncompatibleBrowser?: () => void;
     base64?: boolean;

src/js/pdf.js

@@ -21,7 +21,7 @@ export default {
 
     req.addEventListener('error', () => {
       cleanUp(params)
-      params.onError(req.statusText)
+      params.onError(req.statusText, req)
 
       // Since we don't have a pdf document available, we will stop the print job
     })
@@ -30,7 +30,7 @@ export default {
       // Check for errors
       if ([200, 201].indexOf(req.status) === -1) {
         cleanUp(params)
-        params.onError(req.statusText)
+        params.onError(req.statusText, req)
 
         // Since we don't have a pdf document available, we will stop the print job
         return