Upgrade to Freemarker 2.3.30

Closes gh-20650

Author: snicoll

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -62,7 +62,7 @@
 		<ehcache3.version>3.8.1</ehcache3.version>
 		<embedded-mongo.version>2.2.0</embedded-mongo.version>
 		<flyway.version>6.0.8</flyway.version>
-		<freemarker.version>2.3.29</freemarker.version>
+		<freemarker.version>2.3.30</freemarker.version>
 		<elasticsearch.version>6.8.7</elasticsearch.version>
 		<glassfish-el.version>3.0.3</glassfish-el.version>
 		<glassfish-jaxb.version>2.3.2</glassfish-jaxb.version>