Bump @docusaurus/core from 2.0.0-alpha.58 to 2.0.0-alpha.59 (#611)

Bumps [@docusaurus/core](https://github.com/facebook/docusaurus) from 2.0.0-alpha.58 to 2.0.0-alpha.59.
- [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.58...v2.0.0-alpha.59)

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

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

package.json

@@ -13,7 +13,7 @@
   "dependencies": {
     "by-node-env": "^2.0.1",
     "@docusaurus/preset-classic": "^2.0.0-alpha.58",
-    "@docusaurus/core": "^2.0.0-alpha.58",
+    "@docusaurus/core": "^2.0.0-alpha.59",
     "classnames": "^2.2.6",
     "react": "^16.13.1",
     "react-dom": "^16.13.1"