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

Author: npmcdn-to-unpkg-bot

README.md

@@ -74,9 +74,9 @@ const multibase = require('multiubase')
 Loading this module through a script tag will make the ```Multibase``` obj available in the global namespace.
 
 ```html
-<script src="https://npmcdn.com/multibase/dist/index.min.js"></script>
+<script src="https://unpkg.com/multibase/dist/index.min.js"></script>
 <!-- OR -->
-<script src="https://npmcdn.com/multibase/dist/index.js"></script>
+<script src="https://unpkg.com/multibase/dist/index.js"></script>
 ```
 
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