Fix invalid DOM property

_components/header.tsx

@@ -15,7 +15,7 @@ export default function(props: Props) {
       <h1>{ props.title }</h1>
       {props.author &&
         <p style={{ color: "var(--color-brown)" }}>
-          By {props.author.name} on <time datetime={props.date.toISOString()}>{dateFormatted}</time>
+          By {props.author.name} on <time dateTime={props.date.toISOString()}>{dateFormatted}</time>
         </p>
       }
       {props.comp.separator()}