docs(readme): replace npmcdn.com with unpkg.com

Author: npmcdn-to-unpkg-bot

README.md

@@ -105,9 +105,9 @@ var IPFSRepo = require('ipfs-repo')
 Loading this module through a script tag will make the `Unixfs` obj available in the global namespace.
 
 ```html
-<script src="https://npmcdn.com/ipfs-repo/dist/index.min.js"></script>
+<script src="https://unpkg.com/ipfs-repo/dist/index.min.js"></script>
 <!-- OR -->
-<script src="https://npmcdn.com/ipfs-repo/dist/index.js"></script>
+<script src="https://unpkg.com/ipfs-repo/dist/index.js"></script>
 ```
 
 ## Usage