Upgrade mssql driver to version 4

[navarroaxel]

Upgrade to the latest mssql package version 4.1.0.

Version 4 contains breaking changes https://github.com/tediousjs/node-mssql#3x-to-4x-changes

[dereke]

this sounds like a good idea.

also @refractalize we might be able to run tests against MSSQL in CI using this https://hub.docker.com/r/microsoft/mssql-server-linux/

[cameronstubber]

Also now hitting this issue.

[Naturious]

I attacked the issue, looked through everything, and it seems changing Connection to ConnectionPool in mssqlDriver.js is enough. It seems someone else has tried a PR with that change and it couldn't go through because of travis-ci. Can someone walk me through how I should build this with travis?