[代码完善](v2.5): v2.5 beta update Entity.ftl

Closes #334

2.5 Beta 详情：https://www.ydyno.com/archives/1225.html

eladmin-system/src/main/resources/template/generator/admin/Entity.ftl

@@ -63,7 +63,7 @@ public class ${className} implements Serializable {
     @NotNull
         </#if>
     </#if>
-    <#if column.dateAnnotation??>
+    <#if (column.dateAnnotation)??>
     <#if column.dateAnnotation = 'CreationTimestamp'>
     @CreationTimestamp
     <#else>