chore: release 4.1.5 (googleapis#502)

* updated CHANGELOG.md [ci skip]

* updated package.json [ci skip]

* updated samples/package.json [ci skip]

chore: release 4.1.4 (googleapis#487)

* updated CHANGELOG.md [ci skip]

* updated package.json [ci skip]

* updated samples/package.json [ci skip]

chore: release 4.1.3 (googleapis#480)

* updated CHANGELOG.md

* updated package.json

* updated samples/package.json

chore: release 4.1.2 (googleapis#478)

release 4.1.1. of @google-cloud/bigquery

chore: release 4.1.0 (googleapis#451)

* updated CHANGELOG.md

* updated package.json

* updated samples/package.json

chore: release 4.0.0 (googleapis#448)

Release @google-cloud/bigquery v3.0.0 (googleapis#404)

Release v2.1.0 (googleapis#378)

Release v2.0.6 (googleapis#324)