Upgrade to Kotlin 1.3.31

Closes gh-16795

Author: snicoll

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

@@ -138,7 +138,7 @@
 		<junit.version>4.12</junit.version>
 		<junit-jupiter.version>5.4.2</junit-jupiter.version>
 		<kafka.version>2.2.0</kafka.version>
-		<kotlin.version>1.3.30</kotlin.version>
+		<kotlin.version>1.3.31</kotlin.version>
 		<lettuce.version>5.1.6.RELEASE</lettuce.version>
 		<liquibase.version>3.6.3</liquibase.version>
 		<log4j2.version>2.11.2</log4j2.version>