Upgrade to HikariCP 2.4.1

The Java 6 module has been dropped in 2.4. Dependency management for
HikariCP-java6 is retained at the latest available version; 2.3.9.

Closes gh-4171

spring-boot-dependencies/pom.xml

@@ -78,7 +78,8 @@
 		<hazelcast.version>3.5.3</hazelcast.version>
 		<hibernate.version>4.3.11.Final</hibernate.version>
 		<hibernate-validator.version>5.2.1.Final</hibernate-validator.version>
-		<hikaricp.version>2.3.9</hikaricp.version>
+		<hikaricp.version>2.4.1</hikaricp.version>
+		<hikaricp-java6.version>2.3.9</hikaricp-java6.version>
 		<hornetq.version>2.4.7.Final</hornetq.version>
 		<hsqldb.version>2.3.3</hsqldb.version>
 		<httpasyncclient.version>4.1</httpasyncclient.version>
@@ -664,7 +665,7 @@
 			<dependency>
 				<groupId>com.zaxxer</groupId>
 				<artifactId>HikariCP-java6</artifactId>
-				<version>${hikaricp.version}</version>
+				<version>${hikaricp-java6.version}</version>
 			</dependency>
 			<dependency>
 				<groupId>commons-beanutils</groupId>