BAEL-2958: Update elasticsearch demo project

persistence-modules/elasticsearch/src/main/java/com/baeldung/jest/Employee.java

@@ -6,7 +6,7 @@ public class Employee {
     String name;
     String title;
     List<String> skills;
-    int years_of_service;
+    int yearsOfService;
 
     public String getName() {
         return name;
@@ -32,11 +32,11 @@ public class Employee {
         this.skills = skills;
     }
 
-    public int getYears_of_service() {
-        return years_of_service;
+    public int getYearsOfService() {
+        return yearsOfService;
     }
 
-    public void setYears_of_service(int years_of_service) {
-        this.years_of_service = years_of_service;
+    public void setYearsOfService(int yearsOfService) {
+        this.yearsOfService = yearsOfService;
     }
 }