Bump error_prone_core from 2.19.1 to 2.20.0

Bumps [error_prone_core](https://github.com/google/error-prone) from 2.19.1 to 2.20.0.
- [Release notes](https://github.com/google/error-prone/releases)
- [Commits](google/error-prone@v2.19.1...v2.20.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -104,7 +104,7 @@
       it in the properties section of
       https://github.com/google/error-prone/blob/v${errorprone.version}/pom.xml
       -->
-    <errorprone.version>2.19.1</errorprone.version>
+    <errorprone.version>2.20.0</errorprone.version>
     <javac.version>9+181-r4173-1</javac.version>
   </properties>