Security vulnerability for mocha@2.4.5

[robincher]

Issue Summary

There are security vulnerabilities found in mocha@2.4.5 sub-dependencies. The vulnerabilities found are marked as High-severity, so i thought it should bring this up for the team consideration since it will be a pretty straight-forward fix. The recommended fix is to upgrade mocha to version 4 (minimum)

Expected work to be done

1. Update Mocha to version 4 (or 5) in package.json
2. Update travis.yml to ensure travis only run up to node version supported by Mocha version 4 (or 5 the latest)

Steps to Reproduce

1. npm install
2. npm audit
3. Analyse the output.

More information for the vulnerability :
https://snyk.io/test/npm/mocha/2.4.5

Technical details:

• node-http-client Version: master (latest commit: [a341cf3])
• Node.js Version:8.x.x

[robincher]

@thinkingserious I can take this piece of work if you think it's worthwhile for this month :)

[thinkingserious]

Thank you @robincher!