chore(package): update @types/mocha to version 5.0.0 (#165)

Author: greenkeeper[bot]

package.json

@@ -64,7 +64,7 @@
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "^2.2.3",
-    "@types/mocha": "^2.2.46",
+    "@types/mocha": "^5.0.0",
     "@types/node": "^9.4.5",
     "duplexify": "^3.5.3",
     "eslint": "^4.16.0",