Bump @types/showdown from 1.9.4 to 2.0.0 (#9)

Bumps [@types/showdown](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/showdown) from 1.9.4 to 2.0.0.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/showdown)

---
updated-dependencies:
- dependency-name: "@types/showdown"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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readers/tutors-reader-lib/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "@types/remove-markdown": "^0.3.1",
-    "@types/showdown": "1.9.4",
+    "@types/showdown": "2.0.0",
     "@iconify/svelte": "^2.2.1",
     "@tsconfig/svelte": "^2.0.1",
     "crypto-es": "^1.2.7",