Redirect to postgraphile.org and build.graphile.org (#458)

* Redirect to postgraphile.org

* And for build website

Author: benjie

gatsby-browser.js

@@ -0,0 +1,27 @@
+function checkRedirect(inPath) {
+  const path = inPath.replace(/\/+$/, "");
+  if (path === "/postgraphile" || path.startsWith("/postgraphile/")) {
+    const parts = path.split("/");
+    if (!parts[2]) {
+      window.location.replace(`https://postgraphile.org`);
+    } else {
+      if (parts[2] === "introduction") parts.length = 2;
+      parts.splice(2, 0, "4");
+      window.location.replace(`https://postgraphile.org${parts.join("/")}`);
+    }
+  }
+  if (path === "/graphile-build" || path.startsWith("/graphile-build/")) {
+    const parts = path.split("/");
+    if (!parts[2]) {
+      window.location.replace(`https://build.graphile.org`);
+    } else {
+      if (parts[2] === "introduction") parts.length = 2;
+      parts.splice(2, 0, "4");
+      window.location.replace(`https://build.graphile.org${parts.join("/")}`);
+    }
+  }
+}
+
+exports.onRouteUpdate = ({ location, prevLocation }) => {
+  checkRedirect(location.pathname);
+};