chore(deps-dev): bump docusaurus in /microsite (#2455)

Bumps [docusaurus](https://github.com/facebook/docusaurus) from 2.0.0-alpha.63 to 2.0.0-alpha.64.
- [Release notes](https://github.com/facebook/docusaurus/releases)
- [Changelog](https://github.com/facebook/docusaurus/blob/master/CHANGELOG-2.x.md)
- [Commits](https://github.com/facebook/docusaurus/compare/v2.0.0-alpha.63...v2.0.0-alpha.64)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

microsite/package.json

@@ -13,7 +13,7 @@
     "rename-version": "docusaurus-rename-version"
   },
   "devDependencies": {
-    "docusaurus": "^2.0.0-alpha.61",
+    "docusaurus": "^2.0.0-alpha.64",
     "js-yaml": "^3.14.0"
   }
 }

microsite/yarn.lock

@@ -2228,10 +2228,10 @@ dir-glob@2.0.0:
     arrify "^1.0.1"
     path-type "^3.0.0"
 
-docusaurus@^2.0.0-alpha.61:
-  version "2.0.0-alpha.63"
-  resolved "https://registry.npmjs.org/docusaurus/-/docusaurus-2.0.0-alpha.63.tgz#40402d47b18c42b62e93beb78ce06e000cb88312"
-  integrity sha512-R19pAqcTemJMt7Qykd7ogB2i6R86vbE4/vA/l5/Uuh7xg7ixSKOVZ5M7d9uSoX5jCALOwEyp5iJdleznXUVwAw==
+docusaurus@^2.0.0-alpha.64:
+  version "2.0.0-alpha.64"
+  resolved "https://registry.yarnpkg.com/docusaurus/-/docusaurus-2.0.0-alpha.64.tgz#7833960e9d338403894a27b79058aa4076a676d3"
+  integrity sha512-ARCx0GwAvc5qx7AHvRVZidZuoDTfaaGXzgmkU23NahU6jzO/aK2Q1bH8IKNEQ5C2JuDerQ/hHDh80N20ijk82g==
   dependencies:
     "@babel/core" "^7.9.0"
     "@babel/plugin-proposal-class-properties" "^7.8.3"