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

Author: npmcdn-to-unpkg-bot

README.md

@@ -49,9 +49,9 @@ const bitswap = require('ipfs-bitswap')
 Loading this module through a script tag will make the `IpfsBitswap` object available in the global namespace.
 
 ```html
-<script src="https://npmcdn.com/ipfs-bitswap/dist/index.min.js"></script>
+<script src="https://unpkg.com/ipfs-bitswap/dist/index.min.js"></script>
 <!-- OR -->
-<script src="https://npmcdn.com/ipfs-bitswap/dist/index.js"></script>
+<script src="https://unpkg.com/ipfs-bitswap/dist/index.js"></script>
 ```
 
 ## Usage