Upgrade to Caffeine 2.3.4

Closes gh-7283

spring-boot-dependencies/pom.xml

@@ -51,7 +51,7 @@
 		<assertj.version>2.5.0</assertj.version>
 		<atomikos.version>3.9.3</atomikos.version>
 		<bitronix.version>2.1.4</bitronix.version>
-		<caffeine.version>2.3.3</caffeine.version>
+		<caffeine.version>2.3.4</caffeine.version>
 		<cassandra-driver.version>2.1.9</cassandra-driver.version>
 		<classmate.version>1.3.3</classmate.version>
 		<commons-beanutils.version>1.9.2</commons-beanutils.version>