Fix integration tests on CircleCI

[timleslie]

The new version of Cypress installs its binary application in a global cache

cypress-io/cypress#1300

This causes builds on circleCI to fail, as they cannot find the install on a fresh machine.

This PR updates our config file to put this cache within the node_modules directory so that the package cache mechanism works correctly.

[jesstelford]

The Cypress docs suggest setting ~/.cache as a cache dir on CircleCI: https://docs.cypress.io/guides/guides/continuous-integration.html#CircleCI

      - save_cache:
          paths:
            - node_modules
            - ~/.cache

[dominikwilkowski]

Yeah @jesstelford but to actually keep a cache between installs we need to have it either inside the node_modules folder or create a new cache... Both is viable and this seems not wrong.

[jesstelford]

🎉

[JedWatson]

Quick heads-up @timleslie, remember to delete branches when you merge PRs otherwise they stay around forever and it gets hard to manage