Bump @babel/plugin-proposal-class-properties from 7.5.5 to 7.7.4 (#34)

Bumps [@babel/plugin-proposal-class-properties](https://github.com/babel/babel) from 7.5.5 to 7.7.4.
- [Release notes](https://github.com/babel/babel/releases)
- [Changelog](https://github.com/babel/babel/blob/master/CHANGELOG.md)
- [Commits](https://github.com/babel/babel/compare/v7.5.5...v7.7.4)

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

package.json

@@ -34,7 +34,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.2.2",
-    "@babel/plugin-proposal-class-properties": "^7.2.2",
+    "@babel/plugin-proposal-class-properties": "^7.7.4",
     "@babel/plugin-proposal-decorators": "^7.2.2",
     "@babel/plugin-proposal-nullish-coalescing-operator": "^7.4.4",
     "@babel/plugin-proposal-optional-chaining": "^7.2.0",