Upgrade docusaurus

Summary:
Upgrade docusaurus version. This one opens all external links in new tabs so you don't need to remember to do that yourself.
In static docs, all external links must do this, so this makes it no longer error prone.

Reviewed By: nikoant

Differential Revision: D21815718

fbshipit-source-id: c89a17daeb2bace3e14e0997e7442abc032aef89

website/docusaurus.config.js

@@ -81,7 +81,7 @@ const siteConfig = {
     '/js/google-analytics.js',
   ],
   stylesheets: [],
-  plugins: ['docusaurus-plugin-internaldocs-fb'],
+  plugins: [require.resolve('docusaurus-plugin-internaldocs-fb')],
   presets: [
     [
       '@docusaurus/preset-classic',

website/package.json

@@ -11,8 +11,8 @@
   },
   "devDependencies": {
     "@babel/parser": "^7.8.3",
-    "@docusaurus/core": "^2.0.0-alpha.54",
-    "@docusaurus/preset-classic": "^2.0.0-alpha.54",
+    "@docusaurus/core": "^2.0.0-alpha.56",
+    "@docusaurus/preset-classic": "^2.0.0-alpha.56",
     "classnames": "^2.2.6",
     "docblock-parser": "^1.0.0",
     "docusaurus-plugin-internaldocs-fb": "^0.3.1",