Update @types/mocha requirement from ~2.2.32 to ~5.2.7

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

Author: dependabot-preview[bot]

package.json

@@ -58,7 +58,7 @@
     "prepublish": "rc-tools run guard"
   },
   "devDependencies": {
-    "@types/mocha": "~2.2.32",
+    "@types/mocha": "~5.2.7",
     "@types/react": "^16.0.19",
     "@types/react-dom": "^16.0.2",
     "async": "^0.9.0",