Fix formatting

Author: rwinch

spring-session-samples/spring-session-sample-boot-mongodb-traditional/src/main/java/org/springframework/session/mongodb/examples/mvc/UserControllerAdvise.java

@@ -16,11 +16,11 @@
 
 package org.springframework.session.mongodb.examples.mvc;
 
+import java.security.Principal;
+
 import org.springframework.web.bind.annotation.ControllerAdvice;
 import org.springframework.web.bind.annotation.ModelAttribute;
 
-import java.security.Principal;
-
 /**
  * {@link ControllerAdvice} to expose user related attributes.
  *