Fix #422 fieldUpload event throws ReferenceError in Firefox

Author: ik9999

src/fields/core/fieldUpload.vue

@@ -20,7 +20,7 @@ import { isFunction } from "lodash";
 export default {
 	mixins: [abstractField],
 	methods: {
-		onChange(){
+		onChange(event){
 			if(isFunction(this.schema.onChanged)){
 				// Schema has defined onChange method.
 				this.schema.onChanged.call(this, this.model, this.schema, event, this);