Bump React, Gatsby, and regenerate yarn.lock

When attempting to run the website in development, after making no
changes, I was greeted with the following error message:

> The above error occurred in the <StoreStateProvider> component:
>    in StoreStateProvider
>    in App

After some digging, I dsocvered I needed to update React, React DOM, and
Gatsby.

See: gatsbyjs/gatsby#19827

Then after resolving the above issue, I found this error message when
actually viewing the development server:

> Error: React-Hot-Loader: AppContainer should be patched

See: gatsbyjs/gatsby#26979

package.json

@@ -22,7 +22,7 @@
     "@types/mdx-js__react": "^1.5.3",
     "@types/react-helmet": "^6.0.0",
     "@types/rellax": "^1.7.3",
-    "gatsby": "^2.24.53",
+    "gatsby": "^2.27.3",
     "gatsby-image": "^2.4.20",
     "gatsby-plugin-catch-links": "^2.3.11",
     "gatsby-plugin-manifest": "^2.4.21",
@@ -38,8 +38,8 @@
     "gatsby-transformer-sharp": "^2.5.16",
     "modern-normalize": "^1.0.0",
     "prismjs": "^1.22.0",
-    "react": "^16.12.0",
-    "react-dom": "^16.12.0",
+    "react": "^17.0.1",
+    "react-dom": "^17.0.1",
     "react-feather": "^2.0.8",
     "react-helmet": "^6.1.0",
     "react-rellax-wrapper": "^1.0.5",