Bump @docusaurus/core from 2.0.0-alpha.49 to 2.0.0-alpha.50 (#455)

Bumps [@docusaurus/core](https://github.com/facebook/docusaurus) from 2.0.0-alpha.49 to 2.0.0-alpha.50.
- [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.49...v2.0.0-alpha.50)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

package.json

@@ -9,7 +9,7 @@
     "deploy": "docusaurus deploy"
   },
   "dependencies": {
-    "@docusaurus/core": "^2.0.0-alpha.49",
+    "@docusaurus/core": "^2.0.0-alpha.50",
     "@docusaurus/preset-classic": "^2.0.0-alpha.49",
     "classnames": "^2.2.6",
     "react": "^16.13.1",