export ValidationError class instead of just type

so can check if a thrown error is instanceof it

Author: Sean Wilson

src/lib/index.ts

@@ -1,5 +1,5 @@
 // Reexport your entry components here
 export { default as default } from "./SchemaForm.svelte";
 export type { JSONSchema7 } from "json-schema";
-export type { default as ValidationError } from "./ValidationError";
+export { default as ValidationError } from "./ValidationError";
 export type { default as UISchema } from "./UISchema";