Update HikariCP to 2.1.0, compile against the Java 6-compatible artifact

For those running applications on Java 8, dependency management for the
Java 8-compatible artifact is also provided.

Closes gh-1721

spring-boot-actuator/pom.xml

@@ -143,7 +143,7 @@
 		</dependency>
 		<dependency>
 			<groupId>com.zaxxer</groupId>
-			<artifactId>HikariCP</artifactId>
+			<artifactId>HikariCP-java6</artifactId>
 			<optional>true</optional>
 		</dependency>
 		<dependency>

spring-boot-autoconfigure/pom.xml

@@ -148,7 +148,7 @@
 		</dependency>
 		<dependency>
 			<groupId>com.zaxxer</groupId>
-			<artifactId>HikariCP</artifactId>
+			<artifactId>HikariCP-java6</artifactId>
 			<optional>true</optional>
 		</dependency>
 		<dependency>

spring-boot-dependencies/pom.xml

@@ -70,7 +70,7 @@
 		<hibernate-entitymanager.version>${hibernate.version}</hibernate-entitymanager.version>
 		<hibernate-jpa-api.version>1.0.1.Final</hibernate-jpa-api.version>
 		<hibernate-validator.version>5.1.2.Final</hibernate-validator.version>
-		<hikaricp.version>1.4.0</hikaricp.version>
+		<hikaricp.version>2.1.0</hikaricp.version>
 		<httpclient.version>4.3.5</httpclient.version>
 		<httpasyncclient.version>4.0.2</httpasyncclient.version>
 		<hornetq.version>2.4.3.Final</hornetq.version>
@@ -486,6 +486,11 @@
 				<artifactId>HikariCP</artifactId>
 				<version>${hikaricp.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>com.zaxxer</groupId>
+				<artifactId>HikariCP-java6</artifactId>
+				<version>${hikaricp.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>commons-beanutils</groupId>
 				<artifactId>commons-beanutils</artifactId>