update mocha

Author: horike37

package-lock.json

@@ -30,7 +30,7 @@
     "eslint-plugin-jsx-a11y": "^2.1.0",
     "eslint-plugin-react": "^6.1.1",
     "istanbul": "^0.4.4",
-    "mocha": "^3.0.2",
+    "mocha": "^5.2.0",
     "mocha-lcov-reporter": "^1.2.0",
     "serverless": "^1.26.1",
     "sinon": "^1.17.5"