refactor(starter): upgrade to new version of gatsby

internal/testing/__mocks__/markdown-remark.ts

@@ -0,0 +1,16 @@
+export default {
+  id: "08870ea6-bdc8-4ec6-bf72-1e7d4488eb72",
+  fields: {
+    slug: "/posts/perfecting-the-art-of-perfection",
+    categorySlug: "/typography",
+  },
+  frontmatter: {
+    date: "2016-09-01",
+    description:
+      "An Essay on Typography by Eric Gill takes the reader back to the year 1930. The year when a conflict between two worlds came to its term. The machines of the industrial world finally took over the handicrafts.",
+    category: "typography",
+    title: "Perfecting the Art of Perfection",
+    template: "post",
+  },
+  html: "",
+};