fixing landing page layout on server render

Summary:
On the first render the landing page was missing a CSS class. This ls probably related to https://github.com/gatsbyjs/gatsby/issues/5136
It is fixed by wrapping the page in a <div>

Reviewed By: priteshrnandgaonkar

Differential Revision: D8660801

fbshipit-source-id: dd1ac4145831f2556e2c7ceeaddb2a423447f833

website/package.json

@@ -6,6 +6,7 @@
   "dependencies": {
     "antd": "^3.2.0",
     "atob": "^2.0.3",
+    "btoa": "^1.2.1",
     "gatsby": "^1.9.158",
     "gatsby-link": "^1.6.34",
     "gatsby-plugin-antd": "^1.0.10",