Further improvements to page prerendering

src/pages/404/config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  title: 'Regexper - Page Not Found'
+};

src/pages/index/config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  title: 'Regexper'
+};