fix: display Updated in posts only when modDatetime > pubDatetime (#258)

* refactor: show update time when modDatetime more recently than pubDatetime

* fix: show wrong date when compare with null modeDate

* refactor: modDatetime type checking & rewrite myDatetime

src/components/Datetime.tsx

@@ -28,7 +28,7 @@ export default function Datetime({
         <path d="M7 11h2v2H7zm0 4h2v2H7zm4-4h2v2h-2zm0 4h2v2h-2zm4-4h2v2h-2zm0 4h2v2h-2z"></path>
         <path d="M5 22h14c1.103 0 2-.897 2-2V6c0-1.103-.897-2-2-2h-2V2h-2v2H9V2H7v2H5c-1.103 0-2 .897-2 2v14c0 1.103.897 2 2 2zM19 8l.001 12H5V8h14z"></path>
       </svg>
-      {modDatetime ? (
+      {modDatetime && modDatetime > pubDatetime ? (
         <span className={`italic ${size === "sm" ? "text-sm" : "text-base"}`}>
           Updated:
         </span>
@@ -46,7 +46,9 @@ export default function Datetime({
 }
 
 const FormattedDatetime = ({ pubDatetime, modDatetime }: DatetimesProps) => {
-  const myDatetime = new Date(modDatetime ? modDatetime : pubDatetime);
+  const myDatetime = new Date(
+    modDatetime && modDatetime > pubDatetime ? modDatetime : pubDatetime
+  );
 
   const date = myDatetime.toLocaleDateString(LOCALE.langTag, {
     year: "numeric",