Fix TSC generating broken .d.ts files

Author: wooorm

lib/index.js

@@ -1,7 +1,15 @@
 /**
  * @typedef {import('unist').Node} UnistNode
  * @typedef {import('unist').Parent} UnistParent
- * @typedef {import('unist-util-is').Test} Test
+ */
+
+/**
+ * @typedef {Exclude<import('unist-util-is').Test, undefined> | undefined} Test
+ *   Test from `unist-util-is`.
+ *
+ *   Note: we have remove and add `undefined`, because otherwise when generating
+ *   automatic `.d.ts` files, TS tries to flatten paths from a local perspective,
+ *   which doesn’t work when publishing on npm.
  */
 
 /**