Change header styles

- Use Hubot Sans font family for author and timestamp.
- Remove italics of subheading.

_components/header.tsx

@@ -14,7 +14,7 @@ export default function(props: Props) {
     <header className="page-header">
       <h1>{ props.title }</h1>
       {props.author &&
-        <p style={{ color: "var(--color-brown)" }}>
+        <p class="author" style={{ color: "var(--color-brown)" }}>
           By {props.author.name} on <time dateTime={props.date.toISOString()}>{dateFormatted}</time>
         </p>
       }

_includes/styles/components/header.scss

@@ -15,7 +15,9 @@ .page-header {
       letter-spacing: -0.02em;
     }
   }
-  p.subheading {
-    font-style: italic;
+  p.author {
+    font-family: var(--font--sans-serif-alt);
+    font-weight: 450;
+    font-stretch: 97%;
   }
 }