chore(package): update mocha to version 6.0.0

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "botkit": "^0.7.2",
     "clone": "^2.1.2",
     "eslint": "^5.9.0",
-    "mocha": "^5.2.0",
+    "mocha": "^6.0.0",
     "nock": "^10.0.2",
     "sinon": "^7.1.1"
   },