Update mocha to 5.2.0

Author: renovate-bot

package.json

@@ -40,7 +40,7 @@
     "eslint-plugin-jsx-a11y": "6.1.2",
     "eslint-plugin-react": "7.11.1",
     "jsdom": "12.2.0",
-    "mocha": "3.5.3",
+    "mocha": "5.2.0",
     "nyc": "13.1.0",
     "react": "15.6.2",
     "react-addons-test-utils": "15.6.2",