fix(build): migrate to using main branch (#38)

* fix(build): migrate to using main branch

* 🦉 Updates from OwlBot

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

packages/google-cloud-essentialcontacts/README.md

@@ -142,8 +142,8 @@ Contributions welcome! See the [Contributing Guide](https://github.com/googleapi
 Please note that this `README.md`, the `samples/README.md`,
 and a variety of configuration files in this repository (including `.nycrc` and `tsconfig.json`)
 are generated from a central template. To edit one of these files, make an edit
-to its template in this
-[directory](https://github.com/googleapis/synthtool/tree/master/synthtool/gcp/templates/node_library).
+to its templates in
+[directory](https://github.com/googleapis/synthtool).
 
 ## License