Update @types/mocha requirement from ~2.2.32 to ~5.2.6

Updates the requirements on [@types/mocha](https://github.com/DefinitelyTyped/DefinitelyTyped) to permit the latest version.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits)

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

package.json

@@ -57,7 +57,7 @@
     "prepublish": "rc-tools run guard"
   },
   "devDependencies": {
-    "@types/mocha": "~2.2.32",
+    "@types/mocha": "~5.2.6",
     "@types/react": "^16.0.19",
     "@types/react-dom": "^16.0.2",
     "async": "^0.9.0",