fix: pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-IONETTY-8367012
- https://snyk.io/vuln/SNYK-JAVA-IONETTY-8707740
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-3152153
- https://snyk.io/vuln/SNYK-JAVA-COMGOOGLEGUAVA-5710356

Author: snyk-bot

pom.xml

@@ -18,7 +18,7 @@
 		<maven.build.timestamp.format>yyyyMMddHHmmss</maven.build.timestamp.format>
 		<timestamp>${maven.build.timestamp}</timestamp>
 		<bukkitVersion>1.12.2-R0.1-SNAPSHOT</bukkitVersion>
-		<bungeeVersion>1.19-R0.1-SNAPSHOT</bungeeVersion>
+		<bungeeVersion>1.21-R0.2</bungeeVersion>
 
 		<sonar.organization>georgh93</sonar.organization>
 		<sonar.host.url>https://sonarcloud.io</sonar.host.url>