npm test fails on windows

[mspears-quotecenter]

After cloning the project to run through the excercises, I noticed that the test script uses an environment variable. We run into this issue a lot here at work, due to devs using macs and windows boxes. This is easily fixed by adding cross-env to a project, and calling it before you set any envs in a script.

Since there wasn't a project specific CONTRIBUTING.md, I wasn't sure if I should open a pr here to make the quick fix. Let me know if I should, if it'd help.