fix(mocha): update mochajs version to reduce vulnerabilities (#1830)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:ms:20170412

Latest report for meanjs/mean:
https://snyk.io/test/github/meanjs/mean

package.json

@@ -54,7 +54,7 @@
     "lodash": "~4.17.4",
     "lusca": "~1.4.1",
     "method-override": "~2.3.8",
-    "mocha": "~3.4.2",
+    "mocha": "~3.5.0",
     "mongoose": "~4.11.3",
     "morgan": "~1.8.1",
     "multer": "~1.3.0",