be compatible with older node versions

For Node 18, the webcrypto compatibility mode has to be explicitly
enabled.

This fixes #65.

src/format/format-factur-x.service.ts

@@ -1,6 +1,6 @@
 import { Textdomain } from '@esgettext/runtime';
 import { Injectable } from '@nestjs/common';
-import crypto from 'crypto';
+import { webcrypto as crypto } from 'crypto';
 import {
 	AFRelationship,
 	PDFArray,