Javascript tests are failing in CI

[phil-davis]

They first failed on 2021-04-10 in the early morning "nightly" drone CI.
Examples:
https://drone.owncloud.com/owncloud/contacts/777/8/6

FAILED TESTS:
  contactModel
    ✖ should match a search pattern in title
      Firefox 76.0.0 (Linux 0.0.0)
    _ is not defined
    formatDateAsRFC6350@js/models/contact_model.js:9:12395
    setProperty@js/models/contact_model.js:9:15618
    categories@js/models/contact_model.js:9:11172
    Contact@js/models/contact_model.js:9:20977
    @js/tests/models/contact_model.js:11:17
    

    ✖ should match a search pattern in address
      Firefox 76.0.0 (Linux 0.0.0)
    _ is not defined
    formatDateAsRFC6350@js/models/contact_model.js:9:12395
    setProperty@js/models/contact_model.js:9:15618
    categories@js/models/contact_model.js:9:11172
    Contact@js/models/contact_model.js:9:20977
    @js/tests/models/contact_model.js:19:17
    

    ✖ should parse a valid avatar
      Firefox 76.0.0 (Linux 0.0.0)
    _ is not defined
    formatDateAsRFC6350@js/models/contact_model.js:9:12395
    setProperty@js/models/contact_model.js:9:15618
    categories@js/models/contact_model.js:9:11172
    Contact@js/models/contact_model.js:9:20977
    @js/tests/models/contact_model.js:26:17
    

    ✖ should ignore an invalid avatar
      Firefox 76.0.0 (Linux 0.0.0)
    _ is not defined
    formatDateAsRFC6350@js/models/contact_model.js:9:12395
    setProperty@js/models/contact_model.js:9:15618
    categories@js/models/contact_model.js:9:11172
    Contact@js/models/contact_model.js:9:20977
    @js/tests/models/contact_model.js:33:17
    

    ✖ should generate proper ISO.8601.2004 date string
      Firefox 76.0.0 (Linux 0.0.0)
    _ is not defined
    formatDateAsRFC6350@js/models/contact_model.js:9:12395
    setProperty@js/models/contact_model.js:9:15618
    categories@js/models/contact_model.js:9:11172
    Contact@js/models/contact_model.js:9:20977
    @js/tests/models/contact_model.js:40:17
    

The errors are similar each night since then:
https://drone.owncloud.com/owncloud/contacts/778/8/6
https://drone.owncloud.com/owncloud/contacts/779/8/6
https://drone.owncloud.com/owncloud/contacts/780/8/6
https://drone.owncloud.com/owncloud/contacts/781/8/6
https://drone.owncloud.com/owncloud/contacts/782/8/6

[micbar]

@JammingBen Can you take a quick look?

[JammingBen]

@janackermann and me are on it 👍 Seems to be related to the firefox instance which is used for the tests.

[AlexAndBear]

Bumping gulp to v4 here to make it work on dev machine with node > 10 as well

[AlexAndBear]

@micbar @phil-davis This originates with the latest version of underscore, they don't deliver an underscore.js anymore, instead underscore-esm.js, underscore-node.jse and underscore-umd.js (which we use). So simply we need just to adjust the karma config here.
I don't know if we use underscore in other apps, but we need to have an open eye here.