Bump error_prone_core from 2.15.0 to 2.16 (GoogleCloudPlatform#1288)

Bumps [error_prone_core](https://github.com/google/error-prone) from 2.15.0 to 2.16.
- [Release notes](https://github.com/google/error-prone/releases)
- [Commits](google/error-prone@v2.15.0...v2.16)

---
updated-dependencies:
- dependency-name: com.google.errorprone:error_prone_core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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pom.xml

@@ -60,7 +60,7 @@
 		<maven-checkstyle-plugin.version>3.2.0</maven-checkstyle-plugin.version>
 		<checkstyle-rules.version>9.3</checkstyle-rules.version>
 		<asciidoctor-maven-plugin.version>2.0.0</asciidoctor-maven-plugin.version>
-		<errorprone.version>2.15.0</errorprone.version>
+		<errorprone.version>2.16</errorprone.version>
 
 
 		<!-- All checks except for javadoc enforced by default -->