chore: release 3.15.4 (#535)

🤖 I have created a release \*beep\* \*boop\*
---
### [3.15.4](https://www.github.com/googleapis/nodejs-asset/compare/v3.15.3...v3.15.4) (2021-08-11)


### Bug Fixes

* **build:** migrate to using main branch ([#534](https://www.github.com/googleapis/nodejs-asset/issues/534)) ([30fa2c4](https://www.github.com/googleapis/nodejs-asset/commit/30fa2c48abe3de2a9482ea5bde9a4f315a726b89))
---


This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

asset/snippets/package.json

@@ -15,7 +15,7 @@
     "test": "mocha --timeout 180000"
   },
   "dependencies": {
-    "@google-cloud/asset": "^3.15.3",
+    "@google-cloud/asset": "^3.15.4",
     "@google-cloud/bigquery": "^5.5.0",
     "@google-cloud/compute": "^2.0.0",
     "@google-cloud/storage": "^5.0.0",