Upgrade dependencies

[swyrik]

Make sure that:

• You have read the contribution guidelines.
• You specify the logstash-gelf version and environment so it's obvious which version is affected
• You provide a reproducible test case (either descriptive of as JUnit test) if it's a bug or the expected behavior differs from the actual behavior.

[swyrik]

Please update the log4j 2 version to the log4j 2.17.0 and above. As the current versions are susceptible to CVE-2021-44832 Security Vulnerability.

affected versions: logstash-gelf-1.14.0.jar, logstash-gelf-1.14.1.jar