add additional "tests" to config.yml

[thescientist13]

CircleCI builds the project's Dockerfile as part of continuous Integration. Additional steps in
config.yml should be added to exercise some commands against a fixture.

1. Clone a NodeJS project at a tag like https://github.com/thegreenhouseio/angular-webapp-seed
2. Install dependencies - yarn install (npm install too?)
3. Run the build yarn run build
4. Run unit tests yarn run test