Fix wrong use of slf4j

Closes gh-6650

Author: snicoll

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/RedisSessionConfiguration.java

@@ -18,8 +18,8 @@
 
 import javax.annotation.PostConstruct;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
@@ -45,8 +45,7 @@
 @Conditional(SessionCondition.class)
 class RedisSessionConfiguration {
 
-	private static final Logger logger = LoggerFactory
-			.getLogger(RedisSessionConfiguration.class);
+	private static final Log logger = LogFactory.getLog(RedisSessionConfiguration.class);
 
 	@Configuration
 	public static class SpringBootRedisHttpSessionConfiguration