style : 불필요한 중괄호 제거

Author: ASak1104

src/main/java/team/marco/voucher_management_system/repository/JdbcCustomerRepository.java

@@ -113,8 +113,7 @@ private Map<String, Object> customerToMap(Customer customer) {
     }
 
     private Map<String, Object> getCustomerFields(Customer customer) {
-        Map<String, Object> customerFields = new HashMap<>() {
-        };
+        Map<String, Object> customerFields = new HashMap<>();
 
         customerFields.put("id", customer.getId().toString().getBytes());
         customerFields.put("name", customer.getName());