chore(package): update @types/mocha to version 5.2.1

Closes #265

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
   },
   "devDependencies": {
     "@types/form-data": "^2.2.1",
-    "@types/mocha": "^2.2.45",
+    "@types/mocha": "^5.2.1",
     "codecov": "3.0.0",
     "dateformat": "3.0.3",
     "execa": "0.10.0",