Merge pull request #103 from ButterCMS/update_cdn_link

fix: update cdn link in readme

README.md

@@ -20,7 +20,7 @@ Butter can also be included directly in HTML:
 
 <!-- {x-release-please-start-version} -->
 ```html
-<script src="https://cdnjs.buttercms.com/buttercms-2.1.3.min.js"></script>
+<script src="https://cdn.jsdelivr.net/npm/buttercms@2.1.3/dist/butter.min.js"></script>
 ```
 <!-- {x-release-please-end} -->