Rename ContactUs and Showcases pages to kebab-case to fix broken links

Author: as-ascii

src/pages/ContactUs.js src/pages/contact-us.jssrc/pages/ContactUs.js renamed to src/pages/contact-us.js

@@ -11,4 +11,4 @@ export default function Showcases() {
       </main>
     </Layout>
   );
-}
+}